Natural History. NOTES FOR THE YOUNG MOL. LUSCS.

Otago Witness, Issue 1489, 29 May 1880, Page 26

Natural History. NOTES FOR THE YOUNG MOL. LUSCS.

By Unolb David.

(Specially written for the Otago Witness,)

The next group which presents itself to us contains animals which are very different in their appearanqe from the Articulata d soribed in my last article. Instead of having their body divided into numerous segments, furnished with jointed limbs and having an external skeleton, the Molluscs are either quite naked and defenceless, or else have their bodies covered by shells, in whioh they live, and are generally called, " shell fish." But do not mistake me, my young friends, they are no more fish than insects are. They are known by thiß name to so many of the common people, however, that even naturalists, when speaking in homely language, call them "shell fish." In ancient times, the animals whioh formed and lived in these shells were scarcely known, and little or no attention was paid to them. It was the shells only that attracted the attention of students, and hence the study of this branch of natural

soience received the name of Conchology, a word derived from two Greek words, conch % Bhell, and logos a discourse. But now-a-days, the animal within the shell receives an equal share of attention. And in fact the arrangement of the shells themselves depends almost entirely upon the structure of the animals which form them. A mollusc may be described as a soft, fleshy animal, having neither bones, nor internal skeleton of any kind, and whose body is not divided— like insects and worms —into segments or jointed limbs. Its body is covered with a very sensitive skin, which has the power of drawing itself together. The skin is continually moistened by a sticky liquor, whioh flows out through its pores, and in some instances quite enough to form folds that enrobe the creature as completely as in a mantle. Some molluscshave no shell, then the mantle is thick and sticky, as in the common slug. But the greater number have their bodies protected by shells ; in these the mantle is very delicate and quite transparent, as may be seen in the cockle, mussel, oyster, &c. Many of the mollusos live upon the land, and breathe air— the snail ifa a good example ;— but most of the class live entirely in the sea, deriving therefrom their nurishment, and breathing the oxygen, oontained in the water, by means of branchiae, or gill-like appendages. The study of these oreatures is a most interesting one. Which of you have not been struck with the exquisite beauty, and rare cenformatlon of the many shells that are to be found lining our coast? But the shells on the New Zealand coaßb are not to be compared with those found In warmer seas. As a rule, we find animal life on a larger and grander soale In warm countries than in those that are cold. This rule holds good also in the case of " shell fish." There we find shells large enough to make a bath for a little boy or girl. Thesa are the clam shells, and are the giants of tbe race. I have read that in 1 Roman Catholic countries these shells are sometimes ussd as ■ vessels for holding holy water. " A pair so üßed may be seen in the Church of St. Sulpioe, in Paris, whioh weigh 5001b, and are more than two feet across." Captain Flinders, alluding to these shells, observes :— "Many enormous cockles were scattered upon different parts of the reef. At low water, this cookie seems most commonly to lie half open, but frequently oloses with much noiße, and the water within the shells then spouts up into a stream three or four feet high. It was from this noise and the spouting of the water that we discovered them, for in other _ respeots they were scarcely to be distinguished from the coral rock. A number of these oockles were taken on board the ship and stewed in the coppers, but they were too rank to be agreeable food,, and were eaten by few." Should any of my young friends in the country visit the Otago Museum, they will find one of these shells at the north end of the second , floor. This is a small one, being barely 18

inches across, and something under 1501b weight. Small though it be, it is well worth a visit. The group Mollusoa is divided into two subdivisions. The firßt contains .those animals that have an imperfect nervous system, and which have no heart, or an imperfect one. To this division belong the sea viat (Flustra) and the sea squirt (Ascidia) j also the lamp shells (Terebratula), foßsils of which are found plentifully in the Waihola Gorge limestone. The second is characterised by a more complete nervous system, and ,by having a well developed heart of at least two chambers. The four classes of this subdivision are represented by the oyster, the snail; the" clio (whale feed) j and the last by the ootopus, whose singular appearanoe and habits I have already described.

[The above should have appeared in our last wsue, instead of the " Notes on vertebrata," which was inserted in error.]