On the New Zealand Lamprey, Geotria australis Gray. Part III. The Loss of the Mid-gut Diverticula of the Ammocoetes Stage at Metamorphosis.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 62, 1931-32, Page 120

On the New Zealand Lamprey, Geotria australis Gray. Part III. The Loss of the Mid-gut Diverticula of the Ammocoetes Stage at Metamorphosis. By F. G. Maskell, Ph.D., Lecturer in Zoology, Victoria University College, Wellington, New Zealand. [Read before the Wellington Philosophical Society, 24th July, 1929; issued separately, 30th September, 1931.] 1.—Introduction. 2.—Description of Stages. 3.—Summary. 1. Introduction. In the preceding paper (Part II) of this series, the writer described a pair of mid-gut diverticula found in the Ammocoetes stage of Geotria australis. These diverticula appear to be unique in kind, since they are not known in any other lamprey, nor have they been described before in Geotria (Ammocoetes stage). They are characterised by the presence in their walls of glandular cells, which seem to be comparable with the exocrinous pancreatic cells of Vertebrates. Further, in Geotria no trace of these diverticula is to be found after the completion of metamorphosis by the Ammocoetes. It thus becomes a matter of interest to follow their fate during the process of metamorphosis. During the months of January and February in 1928 and 1929, specimens undergoing metamorphosis, about twenty-five in all, were collected from various rivers in the Wellington district. After examination of this material, nine specimens were selected and these will be described below to illustrate representative stages in the reduction of the diverticula and in the changes in associated organs. The specimens were dissected and the complex of organs in question drawn and later sectioned. The serial sections served to elucidate some of the finer points, which could not be made out in dissection. Again I am indebted to Professor H. B. Kirk for his helpful criticism. 2. Description of Stages. Stage 1.—This stage represents the condition, typical of the Ammocoetes, before any signs of metamorphosis have appeared. The figures (Figs. 1a and 1b) are taken from a 9 cm. Ammocoetes. As this condition has been fully described in Part II of this series, only the essential points are referred to here. The two mid-gut diverticula, structures peculiar to the Ammocoetes stage of Geotria, originate at the junction of oesophagus and mid-gut. The left diverticulum is about half the length of the

oesophagus and lies alongside it. Into this diverticulum, upon its dorsal surface and near its anterior end, opens the bile-duct. The right diverticulum is short and concealed in dorsal view by the posterior portion of the liver. A gall-bladder is present in the liver. The mesenteric artery crosses the oesophagus dorsally in close relation to the bile-duct and then runs alongside the left diverticulum, finally entering the spiral fold. The spiral fold starts in the mid-ventral line at the junction of oesophagus, diverticula, and mid-gut. The gut-vein runs dorsal to the gut on the side opposite to the spiral fold. A short distance posterior to the junction, it receives a large branch from the dorsal wall of the mid-gut and then continues forward as the portal vein to the liver, in which organ it breaks up. Stage 2 (9.5 cms. specimen).—This (Fig. 2) represents a stage in early metamorphosis. The left diverticulum is somewhat reduced in length, the right considerably reduced. The bile-duct still retains its opening into the left diverticulum, and the gall-bladder is present. In the substance of the liver, just beneath its dorsal surface and about half-way down its length, are some conspicuous venous lacunae, not shown in the drawing, but noticeable in sections. In other features this specimen resembles fairly closely stage 1. Stage 3 (10 cms. specimen).—In this specimen (Fig. 3) the junction is no longer found at the same level as the posterior tip of the liver, but some distance anterior to this. Further reduction of the left diverticulum is noticeable; it is now about half its original length and its anterior half overlies the oesophagus instead of being alongside it (compare Fig. 1a). The right diverticulum is very short, having a separate lumen for seventeen sections only (each section seven microns thick); it is now ventral to the oesophagus. The bile-duct opens into the anterior tip of the left diverticulum, instead of upon its dorsal surface. The gall-bladder, although reduced, is still evident in sections. The spiral fold begins at the junction, but on the left side now. The new portal vein, which is to replace the old one, can be traced in sections at this stage. It can be followed from the left diverticulum forwards, across the oesophagus in close relation with the mesenteric artery and bile-duct, to the venous lacunae already noted in stage 2 in the dorsal surface of the liver. This new portal vein is found later to be continuous with the vein of the spiral fold (intra-intestinal vein), and may be regarded as an anterior extension of this latter. The old portal vein is still present. Stage 4 (10.1 cms. specimen).—The junction it situated further forward than in stage 3 and the left diverticulum is very short (Fig. 4). The right diverticulum has a separate lumen in only six sections (these sections, and all others, seven microns thick each) and lies partly ventral to the oesophagus. The bile-duct is short and transversely placed; its opening into the left diverticulum is evident in sections. The gall-bladder with a much reduced lumen is also

evident in sections. The spiral fold now begins on the left side. The new portal vein may be traced in sections from the spiral fold, alongside the left diverticulum, across the oesophagus and into the liver. The old portal vein is present. It will be obvious from the changes in position of right diverticulum and spiral fold, and from the forward movement of the junction, that a process of spiral rotation of the gut is beginning. It appears from stages 3 and 4 that the left diverticulum may lag behind at first in this process, but in the following stage (intermediate between 4 and 5) the left diverticulum has rotated through an angle of 90°, just as right diverticulum and spiral fold have. Here follows a specimen, which is intermediate between stages 4 and 5. The liver region was fixed and sectioned, but not drawn, hence it can be described only from serial sections. The specimen was 9 cms. long and represents the only one actually caught with the diverticula respectively dorsal and ventral to the oesophagus. In this intermediate stage the left diverticulum is short, and throughout its length is dorsal to, i.e., overlies the oesophagus, instead of being alongside it. The right diverticulum is now ventral to the oesophagus and has a separate lumen in fourteen sections. The spiral fold starts on the left side. Gall-bladder and bile-duct are present. Stage 5 (10.1 cms. specimen).—The junction (Fig. 5) is found in about the same position as in stage 4. The rotation of the gut has progressed so far that the originally left diverticulum now lies on the right side of the oesophagus and the originally right diverticulum on the left side. The left diverticulum has crossed the oesophagus dorsally, the right has crossed the oesophagus ventrally. The left (now right) diverticulum is about the same length as in stage 4. The right (now left) diverticulum is represented in this specimen as a mass, RD, visible to the naked eye, but found, when sectioned, to contain no lumen and to consist mainly of islets or follicles of Langerhaus. These islets are referred to more fully in the summary. However, in three other specimens at the same stage, the right (now left) diverticulum shows an independent lumen in from seven to fourteen sections. The very short bile-duct is now on the right side of the oesophagus; of the four specimens at this stage, one shows the bile-duct clearly opening into the left (now right) diverticulum, in the other three this opening can no longer be seen. The gallbladder is present with a reduced lumen. The spiral fold begins at the junction in the mid-dorsal line; in it run the new portal vein (dorsal) and the mesenteric artery (ventral). The new portal vein leaves the spiral fold, accompanies the mesenteric artery as far as the anterior tip of the left (now right) diverticulum and then enters the dorsal surface of the liver. The old portal vein is present and slightly dilated at its entrance into the liver. Stage 6 (10.1 cms. specimen).—The junction (Fig. 6) is nearer the anterior margin of the liver than in stage 5. The left (now right) diverticulum possesses an independent lumen during forty

sections; it tends to lie partly ventral to the oesophagus. The right (now left) diverticulum has an independent lumen in three sections; it now lies dorsal to the oesophagus. A small gall-bladder is present. Traces of the bile-duct persist, but there is no continuous lumen. The spiral fold begins at the junction near the mid-dorsal line and slightly to the right; a little farther back it lies more to the right side. The new portal vein and the mesenteric artery are as in the preceding stage. The old portal vein persists; the anterior tributary, which it receives from the mid-gut, as it enters the liver, probably represents the tributary shown in Figs. 1, 2, and 4. This tributary could not be made out in Figs. 3 and 5. Stage 7 (Specimen not measured).—This specimen (Fig. 7) appears very similar to stage 6, but serial sections reveal several advances. A small gall-bladder is still present, but it is lined by a tall columnar epithelium and its lumen is filled by a coagulum. There is no trace of the bile-duct. The diverticulum, originally on the left, later on the right (Figs. 5 and 6) is now ventral to the oesophagus and has a lumen in one section only. The originally right, later left, diverticulum is now dorsal to the oesophagus; it shows a lumen in three sections. The spiral fold begins on the right side; farther back it is more ventral in position. Mesenteric artery, old portal vein and new portal vein are as in stage 6. The future insular organ, IO, a mass of islets or follicles of Langerhans, is indicated on the left side at this stage. Stage 8 (9.8 cms. specimen).—In this stage (Fig. 8) the junction of oesophagus and mid-gut occurs at about the level of the anterior margin of the liver. There are no traces of diverticula, gall-bladder, or bile-duct. The spiral fold begins in the mid-ventral line; in it runs the mesenteric artery. Beneath the mesenteric artery and attached both to spiral fold and to dorsal surface of liver, is the new portal vein. The portal vein thus attaches the mid-gut to the dorsal surface of the liver. Remnants of the old portal vein still persist, P.V. Sections show that the posterior part of the oesophagus is now solid, with the exception of a few vacuoles in it; the animal must therefore be incapable of feeding. This posterior solid portion projects back a short distance into the lumen of the mid-gut; it is, as it were, being swallowed by the mid-gut. Stage 9 (9.3 cms. specimen).—This is the Macrophthalmia stage; metamorphosis is complete, both externally and internally (Fig. 9). The junction of oesophagus and mid-gut is found above the pericardium and before the anterior margin of the liver. The oesophagus, provided now with a lumen, appears as if invaginated for a short distance into the right side of the most anterior portion of the mid-gut, into which it opens. The spiral fold commences in the mid-ventral line.

The liver is more or less flattened on its dorsal surface; it is much elongated compared with earlier stages; the intestine lies in a slight depression (concavity) on its dorsal side; the liver throughout its length is attached to the ventral wall of the intestine; this attachment is effected by the new portal vein, which lies below the intestine (spiral fold) and above the liver, but attached to both. The mesenteric artery originates from the right side of the dorsal aorta at about the level of the insular organ, runs parallel with the right anterior dorsal prolongation of the liver, enters the substance of the liver and finally, the spiral fold. No traces of diverticula, gall-bladder, or bile-duct are to be found, nor any remnants of the old portal vein. The islets of Langerhans form now a compact organ (insular organ of Cotronei, 1927), at the left side of the oesophagus, just before it opens into the mid-gut. In Geotria there are no indications of dorsal and ventral (Krause 1923) or cranial and caudal (Keibel 1927, Boenig 1928, 1929) portions of this organ, such as have been described in European lampreys. Here the follicles or islets of Langerhans form a single compact organ. 3 Summary. Metamorphosis of the Ammocoetes of Geotria occurs in New Zealand (Wellington district) during January, February, and March, and usually when a length of about ten centimetres has been reached. The changes which take place during metamorphosis in the region of the liver are summarised below. a The mid-gut diverticula, peculiar to the Ammocoetes stage of Geotria, become gradually reduced and finally disappear completely as such. The glandular cells, exocrinous pancreatic cells, which characterise the diverticula and which were described in Part II of this series, are lost also, of course, in this process. During the reduction of the diverticula, however, islets or follicles of Langerhans (referred to below) are budded from their walls. b Before metamorphosis, the oesophagus joins the mid-gut near the posterior tip of the liver; after metamorphosis, this junction is at the level of the anterior margin of the liver. c In the liver region, a spiral rotation of the gut occurs in such a way that (1) the originally left diverticulum appears to crossophagus dorsally, coming to lie first on the right side of, but later ventral to the oesophagus; (2) the originally right diverticulum crosses the oesophagus ventrally to the left side, later becoming dorsal in position. d The spiral fold in the Ammocoetes begins in the mid-ventral line at the junction of oesophagus, diverticula, and mid-gut. During metamorphosis, as a result of the forward spiral growth of the mid-gut, it begins successively (1) on the left side; (2) dorsally; (3) on the right side; and finally (4) in the mid-ventral line again (metamorphosis complete), thus having completed a full

turn and also having advanced considerably further forward on account of the spiral nature of the turn. e The mesenteric artery in the Ammocoetes crosses the oesophagus dorsally from right to left and accompanies the left diverticulum before entering the spiral fold, which begins at the junction near the posterior tip of the liver. After metamorphosis, this artery enters the spiral fold from the right side and near the anterior border of the liver, where the junction is now situated. f The bile-duct, which at first (Ammocoetes) crosses the oesophagus from right to left in close relation with the mesenteric artery and opens into the left diverticulum, is later found much reduced in length and on the right side only (Fig. 5). Finally, it disappears completely. g The gall-bladder is gradually reduced in size and finally completely lost. The epithelium lining the gall-bladder is (1) much flattened in young Ammocoetes; (2) cubical to columnar in large Ammocoetes; (3) composed of tall columnar cells in the second half of metamorphosis. h The liver increases considerably in length and its shape somewhat alters. i A new hepatic portal vein is substituted for the old one. In the Ammocoetes the gut vein (sub-intestinal vein) runs alongside the mid-gut and receives a large tributary from the dorsal wall of the mid-gut a short distance behind the junction (Fig. la). From here it continues forward as the portal vein, entering the posterior tip of the liver. Sub-intestinal vein and portal vein are lost during metamorphosis. The vein of the spiral fold (intra-intestinal vein) forms the new portal vein. During the earlier stages in metamorphosis it may be followed (in serial sections) from the spiral fold forward, alongside the left diverticulum and across the oesophagus in close relation with bile-duct andmesenteric artery to the dorsal surface of the liver. After rotation, it enters the liver direct from the spiral fold. j The islets or follicles of Langerhans are microscopic, hence are not seen in dissections and are not represented in the drawings. Only towards the close of metamorphosis, when the islets become closely aggregated, do they form a mass, IO, the Insular Organ (Cotronei 1927), visible to the naked eye (Figs. 7, 8, and 9). Thus, at the completion of metamorphosis the islets form a single compact organ, which is embedded on the left side in the wall of the gut just before the junction of oesophagus and mid-gut (Fig. 9). As indicated before, there are no signs of separate cranial and caudal portions of this organ, such as are found in European genera after metamorphosis. During metamorphosis the number of islets is considerably increased by the proliferation of fresh islets from the epithelial walls of both diverticula in the region of the junction. As this paper deals mainly with macroscopic features, I have not attempted a detailed account of the islets.

Figs. 1a And 1b.—Dorsal and ventral views of dissections to show diverticula, oesophagus, liver and associated organs in the Ammocoetes stage (9 cms. specimen) before metamorphosis. O E S = oesophagus. A M = mesenteric artery. G B = gall-bladder. B D = bile-duct. L. DIV = left diverticulum. R. DIV = r. diverticulum. P V = portal vein. V H V = ventral hepatic vein. I N T = intestine (mid-gut). S F = spiral fold. Fig. 2.—Stage in metamorphosis—Stage 2. This, and all following stages, represent dorsal views. (9.5 cms. specimen). Lettering as in Fig. 1.

Fig. 3.—Stage 3. (10 cms. specimen). R.D. = swelling caused by remnant of right diverticulum and by islets of Langerhaus budded from it. Lettering as in Fig. 1. Fig. 4.—Stage 4. (10.1 cms. specimen). N P V = region in which new portal vein enters liver. Lettering as in Fig. 1. Fig. 5.—Stage 5. (10.1 cms. specimen). Owing to the process of rotation the originally-left diverticulum (L.DIV) now lies on the right side. Lettering as in Fig. 1.

Fig. 6.—Stage 6. (10.1 cms. specimen). Lettering as in Fig. 1. Fig. 7.—Stage 7. (Specimen not measured). I O = insular organ. Lettering as in Fig. 1. Fig. 8.—Stage 8. (9.8 cms. specimen). Lettering as in Fig. 1. Fig. 9.—Macrophthalmia stage (completely metamorphosed Ammocoetes—9.3 cms. specimen). Lettering as in Fig. 1. Literature Cited. Boenig, H. 1028. Studien zur Morphologie u. Entwicklungsgeschichte des Pankreas beim Bachneunauge, Lampetra (Petromyzon) planeri, Teil 2. Zeitschrift für mikr. anatom. Forschung, Bd. 12, Heft 3–4. —— 1929. Teil 3. Zeitschrift fur mikr. anatom. Forschung, Bd. 17, Heft 1–2. Bronn, H. G. 1905–1924. Klassen und Ordnungen des Tier-Reichs. Bd. 6. Abteilung I. Cotronei, G. 1927. L'organo insulare di Petromyzon marinus. Pubblicazioni della Stazione Zoologica di Napoli, vol. 8. Fasc. I. Keibel, F. 1927. Zur Entwicklungsgeschichte des Vorderdarmes u. des Pankreas beim Bachneunauge, Lampetra (Petromyzon) planeri, u. beim Flussneunauge, Lampetra (Petromyzon) fluviatilis. Zeitschrift fur mikr. anatom. Forschung, Bd. 8, Heft 3–4. Krause, R. 1923. Mikroscopische Anatomie der Wirbeltiere. Vierte Abtllung. Berlin u. Leipzig. Maskell, F. G. 1929. On the New Zealand Lamprey, Geotria australis Gray. Part I—Biology and Life History. Trans. N.Z. Inst., vol. 60. —— 1930. Part II. On the Mid-gut diverticula, the Bile-duct, and the problem of the Pancreas in the Ammocoetes stage. Trans. N.Z. Inst., vol. 61. Nestier, K. 1890. Beiträge zur Anat. u. Entwickl., von Petromyzon planeri. Arch. f. Naturgesch., Bd. 56, Heft I. Schneider, A. 1879. Beiträge zur vergleich. Anat. u. Entwickl. der Wirbeltiere. Berlin.