ZOOLOGY. 525 



fibres, and therefore lie within cavities ; they thus act 

 like as in the feet of Insects. 



The tentacula of many Snails are moved like the feet 

 of Insects ; but as they are not horny, but soft, they are 

 turned either inside out or " vice versa." The oviduct 

 and seminal duct or penis follow the same mode of for- 

 mation. They are likewise everted and inverted. 



3221. These members of the Snail are true Insect- 

 limbs that have remained soft, and are thereupon sus- 

 ceptible of inversion and eversion. Were an Insect's foot 

 soft, every one will admit that it would then yield so as 

 to become inverted, if the fibres pulled upon it. The 

 limbs of Insects have thus only become stiff, and are 

 thereby SnaiPs horns that resist inversion. All these mem- 

 bers are teguments, and give the lie only unto limbs ; 

 for it belongs to the essence of a limb, that it be dense. 



3222. That which suffers eversion or its converse is 

 no limb, but only a sheath, a prepuce. Nearly the whole 

 Snail is but a prepuce, a " membrum virile" or " verge." 



3223. There is no class of animals, in which the testes 

 and penis are found so disproportionately developed as 

 in the Snails Orchitic, Penes-animals. 



3224. The vascular and nervous systems are related 

 pretty nearly as in the Mussels. But the heart is fleshy 

 and has, by reason of its unilateral or single branchia, 

 only one auricle also. 



3225. The Snails repeat the Corals in the cylindrical 

 form of the body, the tubular-shaped shell, and the re- 

 turn of the intestine upon itself towards the mouth, as in 

 many Corallines. 



3226. In them also the organ, which virtually corre- 

 sponds to the kidney, appears to be astir, namely, what has 

 been called the calcareous gland, situated within the 

 branchial cavity, and which opens not far from the anus. 



Class 6. Cardiac, Nephritic Animals. 



3227. Hitherto there has been found only a single 

 " cardia," namely, the left or arterial heart, which, re- 

 ceiving the oxygenated blood from the branchiae, propels 



