210 LECTURES OX 



is oval; and loosely reposing within is a bivalve shell of peculiarly 

 graceful shape and delicate sculpture, with abundant room to open 

 and turn round at the pleasure of the animal. This is a "clam," with 

 very long projecting siphon pipes, which fit into the two lobes of the 

 long passage. They are covered with a rough skin, which produces 

 the wrinkles on the surface of the shelly layer. One of these siphons 

 is constantly drawing water into the gill cavity, while the other carries 

 back the waste. When in the cavity, the delicate frills which form 

 the "plate-gills," characterizing the class Lamellibranchiata,* float 

 loosely in the water, aerating the blood in its intricate labyrinth of 

 veins. At the same time the large, flapping lips, which are so enor- 

 mously developed in the bivalves, (like the nose processes in the bats, ) 

 move through the water, tasting its infusorial contents, and choosing 

 from among them what they shall convey to the mouth, whence a 

 highly organized digestive, circulatory, and generative system is at 

 work to transform the animalcules into molluscous life and shell. The 

 animalcules thus transformed excavate these wonderful caverns; how, 

 we shall presently inquire. Here is a living creature entombed from 

 its earliest days, or rather voluntarily entombing itself; hidden from 

 view and from the society of its kindred; maintaining no more con- 

 nexion with the outer world, except at the pipe ends, than a fossil in the 

 paleozoic rocks; and yet see how -its wants are all provided for by this 

 one exception. That little 0-shaped hole maintains within a, structure 

 of such delicate beauty, with its tissues, nerves, blood-vessels, secre- 

 tions, respiratory, and reproductive apparatus, that the due description 

 of them would require a volume to itself, with an atlas of plates requiring 

 the utmost skill of the artist, as well as the most delicate manipulation 

 of the microscopist. Although at the end of a long and often twisted 

 gallery, how fresh is everything in that inner chamber! The best 

 cleaned dwelling room in regal palaces is impure by contrast. No 

 flies make spots upon the ceiling, or mice leave their unfragrant odors 

 behind the wainscot; no closing of windows retains the impure air, 

 or sting of mosquitos disturbs the equanimity of Gastrochcenoid exist- 

 ence. If our solitary friend has not the pleasures of eyesight, he never 

 dreads to see his enemy; nor has lie once suffered from ache in head, 

 tooth, or ear. lie has an inner light of happiness, though his body 

 dwells in the profoundest darkness. lie has no more trouble than a 

 child for the supply of his temporal wants. The all-pervading care 



°The name Acephala has precedence, but expresses nothing distinctive. All the lower 

 classes of Mollusks and Articulates, as well as the v\ hole of the Radiates, arc destitute of that 

 to us necessary appendage. The proper name of every individual (the genus and species) 

 should follow the modified law of priority. But classirication is a matter of opinion, and 

 must change (with the nomenclature founded on it) with advancing knowledge. The name 

 Conchiieia was applied bv Lamarck to the Lamp shells as much as to the Cockles. When 

 these are divided into two classes, it is well to find names which sufficiently express the 

 main differences between them. 'J he Terebratula breathes through pores in the surface of 

 the mantle, while the Anomia, which Linnseus (following the best light of his time) placed 

 in the same genus, breathes by overlapping laminse. Blainville's names, Lamellibranchiata 

 and Palliobranchiata, exactly express this difference; while, as in the case of the Dibranchiate 

 and Tetrabranchiate Cephalopods, these gill differences are co-ordinate with others of great 

 importance in the whole economy of the animals. The name Brachiopoda is very good. 

 though it does not bring out the contrast. 



