^4jfi)dtieH of HelkoUmax. 311 



ihat in the total absence of any evidence to the contrary, we may assume 

 the slructure to be the same. Again in Parmacella there is a slight 

 strangulation of the stomach, but on the whole there is a less perfect 

 resemblance as regards the salivary glands, their form, the point to which 

 they extend, and indeed in the general course of the intestine than in 

 Helix. As the shell of Parmacella is not spiral, of course we must 

 expect corresponding differences as regards the lobes of the liver, one of 

 which is so strongly affected by any change of form in that point. Heli- 

 colimax is nearer then to Helix as regards the digestive organs ; nearer 

 to Parmacella as regards the generative. 



With respect to outward structure, Helicoliniax is intermediate between 

 Helix and Parmacella, but with respect to internal. Helix would be 

 intermediate as regards the digestive organs ; while Parmacella would 

 be intermediate as regards the generative organs. 



Whence this curious result arises, that each in one important point will 

 take a middle place. Hence in the same animal two opposite ends are 

 carried on, in the simplification of one important function, and the com- 

 plication of another. But this takes place not merely by the intervention 

 of a single animal but by an interchanged relation. 



It would have been interesting to have compared the three genera with 

 respect to the nervous system, but I have not sufficient data to go upon, 

 and it could be only done by examining the three together for the express 

 purpose, with the greatest attention, and with every advantage of nume- 

 rous specimens. 



I do not mean to say that these are the only genera with which Helico- 

 limax may be compared, but merely that to these it is related most nearly. 



Helicarion would most likely prove to be almost the same in structure. 

 Of the genera whose structure is described, it is with these it has the 

 nearest affinity. From Tcstucellus it differs especially, in the far lower 

 developement of the retractor muscle of the mouth, which should seem 

 to prove that if it be essentially carnivorous, it is so in a different way. 

 The stomach in Testacellus is well marked and simple, and the generative 

 organs still less complex. It is much more nearly related to Limax, but 

 Limax or rather Arion (for of that alone the anatomy is given in Cuvier's 

 Memoires) is in every respect in which the two differ less complicated, 

 both as to outward and inward form. 



X 2. 



