126 Messrs. Alder and Hancock on the gmvs Eolidina. 



well aware that it would be wrong to infer, in every case, the cor- 

 respondence of internal characters from a similarity of outward 

 form ; but at the same time, when the external characters are so 

 very similar as they are in the present instance, we should be led 

 to expect, that if any difference in the anatomy did exist, it would 

 not be such as to affect the most important animal functions. 

 The two remarkable deviations from the tjqiical organization of 

 the family which M. de Quatrefages points out, are however of 

 this kind. We consider ourselves justified, therefore, in scruti- 

 nizing more narrowly the accuracy of his observations. He com- 

 plains that in asserting that the anus in Eolis is placed in the 

 side, we do not enter into the details which are necessary to un- 

 derstand the relations of this orifice and the intestine proceeding 

 from it with the gastro-vascular system. 



This relationship is very simple. Our observations lead us to 

 the conclusion, that the whole of the food which enters into the 

 stomach does not pass into the gastro-vascular apparatus ; indeed 

 very little of the solid aliment enters it, and such as does is 

 always driven back to the stomach, nothing being allowed to re- 

 main in this complicated system of vessels but the most refined 

 portion of the ])roducts of digestion ; such, in fact, as are capable 

 of being converted into nutrition ; and the mass of the grosser 

 particles is conveyed by a short intestinal canal, crossing diago- 

 nally from the left to the right side of the body where the anus 

 is situated. It is placed a short way behind, and generally a little 

 above the orifice of generation : this we have ascertained beyond 

 a doubt. It is difficult to see the anus when in a state of repose ; 

 but when the intestine is filled with coloured matter, or dui-ing 

 the expulsion of the excrement, it may be very readily observed. 

 In the latter case it is considerably enlarged and protruded into 

 a nipple-shape. Let us now tm-n to M. de Quatrefages^ descrip- 

 tion of these parts in Eolidina. According to his views, the anus 

 is situated posteriorly at the termination of the central vessel of 

 the gastro-vascular system, and connected with it : this central 

 vessel he considers the intestinal canal. It is evident however, 

 that as very little of the solid portions of the nutriment is admitted 

 into those vessels, and as never any of it is allowed to remain 

 there, the anus so placed is not available for the expulsion of the 

 grosser excrementitious matter, and cannot in fact be considered a 

 true anus; indeed M. de Quatrefages himself does not seem to 

 consider it so. If therefore this aperture (which we have not 

 detected in Eolis) does exist, it can only be considered as an ex- 

 cretory orifice, somewhat similar to those that we have found at 

 the ends of the papillae*. 



* Since the publication of our last paper, we have had the opportunity of 

 confirming our observations on the ejection of small bodies from the ends of 



