SCHOOL IN THE OPEN.

Star (Christchurch), Issue 17569, 20 June 1925, Page 23 (Supplement)

SCHOOL IN THE OPEN.

STUDIES IN THE GREAT OUT-OF-DOORS.

(By

J. J. S. Corncs, 8.A., B.Sc.)

The "Star” has arranged with Mr J. J. S. Ccrnes. 8.A., B.Sc., to write a series of illustrated articles which will give teachers and others a fuller appreciation of the Great Out-of-doors. They will deal with various aspects of plant and animal life, as well as with inanimate nature. Questions and material for identification will be welcomed.

THE OCTOPUS AND ITS RELATIVES.

(LXIIJ.) Jn previous articles we have studied two types of molluscs to be found about our shores —first, those with the broad, adhesive foot, -whereby they cling to the rocks against the force of waves, and second, those with the wedge-shaped, ploughshare foot wherewith they burrow down into the sand cf the open beach to avoid being washed ashore by the breakers. The first type is represented by such univalves as limpet, pawa and cat’s eye, or by the armadillo-shells, chitons, to be found on .the rocks between Stunner and Taylor’s Mistake; the second group includes such bivalves as pipi, so abundant on the Brighton beach. But there is in addition a more highly-developed group of moduscs, which make up the " head-footed ” order (Cephalopoda), so called because the mouth is in the middle of the foot, which is divided into eight, ten or more ” arms ” or “ tentacles.” It includes the octopus, cuttlefish, squid, argonaut and nautilus. In this group the nerve-ganglions are centred in a brain, enclosed in a skull of cartilage. The eyes remind one at first of those of a vertebrate, such as a fish or bird : and the horny beak, or the octopus, for instance, appears very like that of the cockatoo. At one time the opponents of the doctrine of evolution used to argue that the occurrence of such familiar structures in a family so unrelated to backboned animals could not be accounted for by any theory of descent, but only by special creation. Closer examination showed, however, that the eyes are no more like our eyes than the camera is, and for the same reason—namely, that all siinple eyes, using the same white light, must have a lens and throw an image on a retina; while as for the beak, the i . >er jaw here closes into the lower, the opposite from the way in birds. We have here

an example of "convergence” in evolution. leading to similar structures in unrelated organisms—the structures are “ analogous,” not ” homologous.” The octopus, or devil-fish, is well known to us, by reputation at least. It is quite common on the East Coast near Kaikoura, and is often speared for bait, or caught on the line, usually hooked through a tentacle when sucking at the bait. It has no internal skeleton nor outer shell. By of its eight arms with their suckers it walks along the sea-bottom. In the case of a bivalve mollusc, such as pipi, a fleshy mantle, which secretes the shell, drapes over the body, and covers a pair of plate-like gills on either side. In the octopus the mantle cavity contains two gills “hooks and eves”; so that when it contracts the water in it is ejected forcibly through a funnel, and the mon with all the group of Cephalopods except Nautilus, it can eject along with the water a dense black ink, " sepia.” which hides the animal in a fog, and. like a smoke screen, covers its retreat from enemies. The cuttlefish has a light internal shell in the dorsal hump. In addition to the eight arms cf “ octopods ” this “ decapod ” has two long tentacles with suckers only at the flattened tips. The shell is used a good deal for fine polishir.g. The squid or -pen and ink fish” has a wider and shorter fin, and the internal shell is redxiced to a horny fiat. pen. It is said that a famous geologist wrote his report from the pen and ink of a squid that died ages ago. The word ” squid ” may come from " squirt To the squids belong the gigantic forms sometimes met with in tropical seas and in the North Atlantic. Saville Kent tells a thrilling story of Newfoundland fishermen, who saw floating on the water a dark mass, which one struck with a boathook. “ Upon the shock the dark mass became suddenly animated, and, spreading out, disclosed a head with large, staring eyes, which seemed to gleam with intense ferocity. The creature at the same time exposed to view and opened its parrot-like beak. The men were petrified villi terror and powerless to stir. “ Before they had recovered their presence of mind the monster, now

but a few feet from the boat, sudden shot from its head several long, _fles! arms, grappling with them for t’ boat, and seeking to envelope it i their folds. Only the two longe reached tbc craft, and these went eci ; pletely over and beyond it. One the men, seizhig his hatchet with desperate effort, severed these with single blow, and the creature disa. pen red beneath the water, leading i the boat its arms as a trophy of tb encounter.” Professor Verrill estimated the tots length of the arms at forty-two feet and the length of the animal to lxav* been sixty feet in all. The Argonaut (Paper “ Nautilus’’’) i ix very famous animal. She appear to have an external shell, but thoug she lives in it she is not fastened t« it, and uses it os an egg-case. Moreover. the shell is uot secreted by mantle, but by the touch of two flattened webbed arms, with which she moulds this beautiful home about herself. Tradition says that hoists these flattened arms c.s sails, but she reallv swims, as clo the others, by squirting water from the funnel. Beautiful small chambered shells, milky-white and curled like a posthorn, are sometimes cast up on our North Auckland beaches. They are tlxe internal shells of Spimla. in life nearly covered by the mantle, though tlxe living creature is rarelv taken. Alb’ed to the Spirilla ai'e the fossil “ Belemnites.” known in England as “ thunderbolts.” All the above cephalonods have two gills in the mantle-cavity. Tlxe four gilled branch of the order is almost extinct. In Meozoic times there were the huge Ammonites; but now there remains only the chambered Nautilus. This lias a truo external shell, made by the mantle, which, as the animal grows, adds to the spiral to fit the widening body. The animal then, to support its body in the shell, builds a pla.tform below? itself ; so the spiral becomes partitioned off into many chambers. These communicate by a canal or “ siphuncle.” which runs centrally, not, as in Soirula, along the inner side of the coil ; and perhaps by regu-

lating the amount of air and water in the chambers the animal changes its specific gravity. It lias more arms than ten : it has no ink-sac, and no complete funnel. IVe began with the octopus, a repulsive creature which recalls the story of an encounter in Victor Hugo’s “Toiler of the Sea,” where it coiled itself about G ill iatt, sickening and paralysing, him with its cold and slimy grasp, and trying to get its beak *n a position to bite and tear. A\o must end on a. hoopier note, with a quotation from Oliver "Wendell Holmes's poem, “ The Chambered Nautilus’ *• Yet after year beheld the silcut toil That spread his lustrous coil. Still, as the spiral grew. He left the past year's dwelling for the new. Stole with soft steps its shining archway through. Sealed up its idie door. Stretched in his last-found home, And knew the old no more.” “Build thee more stately mansions, O mv soul. •While'the dull seasons roll; Leave thy low-vaulted past: Let eacli new chamber, worthier than the last. Shut thee from heaven with a dome more vast, Till thou at length art free. Leaving thine outgrown shell by life's unresting sea.” (To be continued next Saturday.)