ANIMAL KINGDOM. 237 



move by an undulatory motion, and can seize the food of the 

 animal when the oesophagus is turned inside out, which it 

 has the remarkable property of doing. The hermaphro- 

 ditism also of the Bulla differs from that of the Acephala. 

 We are thus prepared for the Aplysia where the branchiae 

 are similarly situated, the gizzard more formidably armed, 

 the hermaphroditism and sexual organs the same as in 

 Bulla. But in this new animal there are four stomachs ; 

 and the head, eyes and tentacula are all equally distinct. 

 By means of the genera Pleurobranchus and Onchidium 

 yve arrive among the Pulmonis of Cuvier. Then proba- 

 bly the chain is to be followed through the Pectini branches, 

 Scutibranches, Cyclobranches, and Inferobranches of Cu- 

 vier, till we have the last form of his Gasteropoda in the 

 genera Doris, Tethys, Glaucus, fyc. Such at least do I 

 imagine to be the path of Nature through the very intri- 

 cate and numerous family of Gasteropoda, whether we 

 take into consideration their general anatomy, or that most 

 important part of it, — the nervous system. This we shall 

 observe gradually getting more collected into one mass 

 from the scattered system of ganglions in Bulla and Aplysia, 

 till we arrive at the concentrated form which the medullary 

 matter assumes in Scyllaa or Doris. There appear how- 

 ever to be exceptions to this regularity ; but whether these 

 are owing to the imperfect state of our acquaintance with 

 their anatomy, or to other causes, is a question yet to be 

 decided. 



To the industry of Cuvier and Poli we owe almost 

 all the knowledge we possess of the internal structure 

 of the Mollusca : but it would be placing greater con- 

 fidence in the observations of these learned men than 

 they are justly entitled to, were we to rest contented with 



