Art. XII.—An Account of the External Anatomy of a Baby Rorqual (Balænoptera rostrata).

Transactions and Proceedings of the Royal Society of New Zealand, Volume 34, 1901, Page 151

Art. XII.—An Account of the External Anatomy of a Baby Rorqual (Balænoptera rostrata). By W. Blaxland Benham, D.Sc., M.A., F.Z.S., Professor of Biology in the University of Otago. [Read before the Otago Institute, 11th June, 1901.] On Monday, 6th August, 1900, I was informed that a “young whale, about 12 ft. long, had been cast ashore on the beach outside the Otago Heads.” It was offered to me for a sum of money, and I arranged to purchase it. It turned out to be a young rorqual, about 10 ft. long overall, in excellent condition, the skin being damaged here and there, partly from being handled no doubt, partly from being cast ashore. On Tuesday I had photographs taken of it in various positions, and, with the help of Mr. Hamilton, made measurements and observations on its outer anatomy. On Wednesday I had a mould taken of it, and was able to commence dissection on

that afternoon while the cast was being made. The cast is now exhibited in the University Museum. Colour: In its general colouration it agrees pretty closely with the description given by Von Haast (Trans., xiii.). The upper surface of head and back is dark-grey—practically black, including dorsal fin and dorsal surface of the caudal fluke. The belly is pure snow-white (which after exposure to rain and air during twenty-four hours became a bluish-white). The lower jaw is very dark-grey, fading rapidly to white a few inches below the gape. Behind the angle of the mouth the colour is paler grey. The pectoral limb dorsally is grey, deepening to black along the posterior margin; but the tint gets lighter towards the anterior margin, which is white. The line of junction between grey and white is about on a level with the mouth, the base of the pectoral limb, and the caudal fluke. But the tone of the grey varies: Above the base of the pectoral are wavy lines of dark and light grey, obliquely vertical, with the upper ends directed backwards, one of which is particularly noticeable, starting from the axilla upwards and backwards; a second, more or less parallel to this, lies above the base of the pectoral. About midway along the body the darker tint is more extensive, invading the generally lighter grey, so as to form an irregularly oval darker patch about midway between pectoral and dorsal fins. Mouth: The roof of the mouth is bright-pink; the baleen, which forms but a narrow band on each side—only about 1 ¾ in. broad at its broadest—is purplish-pink for about half its depth, the free ends—that is, about lower half—being pink. But during the day these colours changed to pink and almost white respectively. The base of the baleen is yellowish. The tongue is pink; the back of mouth pink, with a few black pigment spots. The tongue itself is margined laterally along the region that is free (which is 8 in. in length) with thin fleshy folds, irregular in shape and size, vertically disposed, overlapping one another; soft, flexible, and no doubt an aid in capturing food. Hair: There are about fifteen hairs on each side of the face, and evidence, in the presence of follicles, of five or six more. On the chin, or anterior rounded extremity of the lower jaw, are two vertical rows of hair-follicles, from most of which a single short white hair protruded. Each pit is very distinctly marked, owing to the very dark-grey colour round its margin. The two rows, one of which presented seven the other eight follicular pits, are about ¼ in. apart, though the upper pair of pits are distinctly more widely separated. There is a space of about ¼ in. between each pit of a vertical row. The bristles, of which I counted six on the right and four on the left side, issuing from the upper pits of

each row, are about ⅛ in. long. Along the upper and lower jaws is a horizontal series of similar white hairs of larger size. Along the upper jaw is a row of four bristles, and two or three black hairless follicular pits anteriorly. The first hair is 8 ¾ in. from anterior end of the snout, the last 15 ¾ in., and the series lies about 1 ½ in. above the lower margin of jaw. The hairs on the lower jaw constitute a row of five bristles, the first of which is 10 in. from the anterior end, the last 15 ½ in. The row slopes downward posteriorly, so that, while the first hair is 1 ½ in. below the upper margin, the last is 5 ½ in. below. The hair is ½ in. in length. This line follows, more or less accurately, the line of junction between grey and white. The spaces between bristles, starting from anterior end of series, are: 1 ¾ in., 2 ¾ in., 1 ½ in., 1 ½ in. The baleen is coloured as above. Each row forms an elegant curve close to the outer margin of the roof of the mouth. The right and left rows nearly meet anteriorly, where each is very narrow and the baleen short. The rows then diverge, following the outline of the jaw, but behind the angle of the gape curve inwards for a short distance. The total length of the row, measured in a straight line, is 1 ft. 9 in. The greatest distance separating the rows is 6 ¼ in. This, then, is maximum width of palate. The greatest length of baleen is 4 ¼ in., and this is not the outermost margins; the breadth is 1 ¾ in., which is retained for greater part of course. The animal was a young female, and had not long been born, as the navel was a slit-like depression 2 in. long and about ½ in. deep, with vascular walls; it is situated 5 ft. 4 in. from tip of lower jaw. On each side the skin shows a pink patch a short distance above the navel. The navel is situated in an oval or diamond-shaped area with rounded angles, limited by a shallow furrow, and from the posterior angle a distinct furrow passes backwards to the urino-genital depression, or vulva, which lies 1 ft. 5 in. behind it. This vulva is slit-like, the lips being close together; but this slit, which is 6 ½ in. long, bifurcates posteriorly, leaving a small triangular area, which is the base of a ridge which can be traced forwards into the vestibule. On pressing apart the lips a deep depression is visible, the bottom of which is surrounded by a folded wall. The depression is funnel-shaped, but compressed laterally, and along the anterior and posterior sloping wall a ridge passes downwards towards the bottom. The anterior ridge terminates in a freely projecting subconical clitoris, overhanging the urinary aperture, which is transversely extended and has soft plicated lips. The clitoris is separated from the ridge by a transverse curved furrow. The posterior ridge is at its base more prominent, but gradually diminishes towards the bottom of

the pit; it terminates at the hinder margin of an irregularly rounded vaginal aperture, the lateral margins of which are folded in the usual way. The mammary clefts are situated on either side of the hinder region of the vulva, and about 1 ½ in. from it. Each slit is about 1 in. in length, and is the opening of a pit 1 indeep, from the bottom of which a small rounded nipple rises upwards. Above each mammary cleft, about 1 in. from it, is a shallow furrow parallel with it, marking out with it a slightly rounded area. The anus, which lies a short distance behind the vulva, is 2 ft. 5 in. from the middle cleft of caudal fin. The characteristic gular furrows extend from about 4 in from anterior end of jaw for a distance of 4 ft. 8 in., terminating behind the level of the flipper. There are forty-five furrows between the two flippers, while further forward the number is increased, and at the angle of the mouth eight additional short furrows exist, on each side, dorsal of the longer ones. Each ridge which separates two furrows is ½ in. wide. These ridges are not produced by mere folding of the skin, but are delimited by straight grooves, ½ in. deep, into which the epidermis, of course, dips. But in transverse section of the skin it is evident that the blubber does not share in the folding, for its inner surface is plane, and consequently it is of less thickness below the furrows than below the ridges, where it measures 1 ¼ in. The middle series of furrows are rather shorter than the more laterally placed ones, whose length is given above; the ventral rugæ being 4 ft. 2 ½ in., and beginning 8 ½ in. from chin. Measurements of External Features. Ft. in. Total length from tip of snout to end of fluke, measured over back 10 5 Length of body—i.e., to notch in fluke 10 1 " " (in straight line) 9 9½ Length of upper jaw, tip to angle of gape 1 10 " lower jaw 1 11 Tip of snout to anterior base of pectoral limb 3 2 " axilla 3 9 " base of dorsal fin 6 9 Length of base of dorsal fin 0 8 Height (greatest) of dorsal fin 0 4 Distance from posterior margin of dorsal fin to tip of body—i.e., median notch of fluke 2 8 Distance of vulva from anterior end 7 6 Greatest circumference of body, at a distance of 5 ft. 7 in. from snout 5 2½ Circumference at axilla 4 11½ " middle of dorsal fin (but, of course, excluding it) 3 6 " immediately anterior to root of fluke 1 6½ Weight, about 12 owt. (estimated).

Measurements of Head. Ft. in. Gape 1 10 Tip of snout to anterior corner of eye 1 11 Eye—   Length 0   Height 0 0½ Ear—   Distance from posterior angle of eye 0 5   Length of auditory cleft 0 5 Nostrils (blowholes)—   Tip of snout to anterior end 1 4   Length of nostril 0 3½   Distance between anterior ends 0 2 ¾   " posterior ends 0 4½ Length of median internasal furrow 0 4½ Pectoral fin—   Distance from snout 3 2   Breadth of base 0 7   Length along preaxial margin 1 8   " postaxial margin 1 8   Breadth (greatest) 0 5 Caudal fluke—   Breadth (greatest) at end 2 4   Length, from root* Measured three days after death. The sides had curved somewhat. The length is too great. 1 5   Length, behind end of body* 0 6½ Breadth of body at base of c.f. 0 3½ [After this article was set up I received from Sir William Turner his account of “The Lesser Rorqual in Scottish Seas,” in Proc. R.S. Edin., 1892, xix., p. 36, in which he gives full details of external anatomy of several specimens. I regret that I cannot make use of the facts for comparison.]