MALACOLOGY. 



olfactory tentacula, and, above all, for the ocular 

 ones, whose organisation is much more complex, but 

 with regard to the animal's head, including the brain, 

 sucli a thing is to us quite inconceivable, notwith- 

 standing the solemn assurances of some writers to that 

 effect. We have indeed been asked why the experi- 

 ment was not made by ourselves, to which we reply, 

 that it has been made by others ; and when such 

 men as Muller, Bonnet, and Spallanzani, entertain a 

 contrariety of opinion on the subject, we feel no in- 

 clination to shake our conviction by useless cruelty 

 and needless experiments. The functions of decom- 

 position or exhalation in molluscs nearly resemble 

 that of the higher animals ; general exhalation, which 

 is much more abundant in the aerial than in the aquatic 

 molluscs, appears but little known ; it is probably 

 more passive than active. The particular exhalations 

 constituting the secretions and excretions are rather 

 abundant. We have already spoken of those which 

 form the shell in such as possess it, as also the liver 

 and salivary glands, employed in digestion. 



The means of reproduction in molluscs is not known 

 to us in its full sense, and the investigation belongs 

 to the physiologist. Nothing whatever is positively 

 known of the duration of life in molluscous animals, 

 from the impossibility of watching their progress 

 while in a state of freedom, surrounded by the acces- 

 sories necessary to their development and preserva- 

 tion, but it may be inferred from the length of time 

 necessary to mark their growth that they live long; 

 dwelling also as they do in a medium, and in situations 

 less subject to the changes of atmosphere or various 

 causes that influence the existence of other portions of 

 creation, it is but reasonable to conclude that the mea- 

 sure of their life is less acted upon by extraneous effects, 

 and that they attain to greater ages in proportion to 

 these advantages than any other branch of animated 

 creation. We do know that they possess the power 

 of multiplying their kind to a countless extent, and 

 wherever that exists in creation, great tenacity of life 

 is generally observed as being necessary to keep up 

 the useful purposes they are destined to perform, 

 which invariably are more numerous than in those 

 animals which multiply their race slowly and in small 

 numbers. No species of molluscs, even of the most 

 perfectly organised, exhibit any positive appearance 

 of sympathetic associations, or the slightest mutual 

 attachment, beyond each instinctively seeking the 

 most favourable situations for their development, 

 growth, and comfort. 



We pass overthat partof the physiological structure 

 of these animals but little understood, and only inter- 

 esting to a class of persons who will seek it from 

 higher authorities than ours : we will, however, de- 

 scribe some interesting facts regarding the eggs of 

 molluscs, founded upon the observations of long ex- 

 perience, and many of them not generally known, 

 from the same cause that has and ever must retard 

 the progress of our knowledge in this department of 

 nature we mean the difficulty of watching their oper- 

 ations in their native element. The eggs of nearly 

 every mollusc are mucous, and more or less of a horny 

 texture, but in some of the terrestrial species (the 

 Bidinus, Achatina, $c., for example) they are covered 

 with a calcareous shell, rendering them in appear- 

 ance similar to those of birds, and of some rep- 

 tiles. They are sometimes cast or laid in a congre- 

 gated free mass, in which they are united in several 

 ways ; but sometimes they are deposited singly, and 



attached to marine bodies by means of a stem or 

 pedicle, which occurs in the Buccinum, Vurpura and 

 its congeners, and the females of the ovoviviparous 

 molluscs lay their eggs in small numbers during the 

 season of fine weather. In the eggs, here figured, of 



Eggs of the Argonauta. 



the animal found in the Argonauta argo, they resem- 

 ble a bunch of grapes. In the terrestrial molluscs 

 the eggs appear always sessile, often separated, or 

 merely laid in a heap, and often united by a viscous 

 matter which forms them into a mass. These eggs are 

 generally deposited in situations the most favourable 

 to their future development, and though a very small 

 number of molluscs appear to entertain the slightest 

 kindness for, or take the least care of their progeny, 

 some such feelings may be said to exist in the Voluta 

 gondola, the young of which, according to Adanson, 

 are gathered together during some time in a fold of 

 its foot, probably as they quit the oviduct. The 

 janthina, also, deposits its eggs around the parent 

 shell ; common snails lay theirs invariably in favour- 

 able situations for their best attaining maturity, and 

 the more easily meeting with a supply of naturally 

 wholesome food the moment that want is experienced 

 by a new state of vital existence ; and the mollusc 

 always found in the Argonauta constantly deposits its 

 eggs at the bottom of the shell. The Balani possess 

 the power of placing their eggs by means of the long 

 trunk which terminates their oviduct ; but most mol- 

 lusca lay their eggs by hazard, and the viscous matter 

 usually surrounding them enables their position to 

 be stationary on those spots in which they were first 

 excluded. Various experiments have been made 

 clearly establishing the great vitality of the eggs of 

 molluscs, some of which, after having been five 

 months exposed to the burning sun of a tropical cli- 

 mate, and others to the artificial heat of an oven, and 

 repeatedly dried in it, have not lost the property of 

 future development. 



Of the habitat of molluscs, they may be said to 

 exist in every part of the globe, buried in the impene- 

 trable depth of the sea on the surface of the earth, 



Testacella haliotidea. 



and even one species, the Testacella haliotidea, here 

 figured, under the ground : some of them are to a certain 



