Messrs. Hancock and Eaibleton on the Anatomy of Eolis. 79 



great central trunk, and divide in the same way as the anterior 

 pair, but the branclics diminish in number and in size towards 

 the posterior extremity of the body. It may be remarked, that 

 the tirst and second pairs of branches in this and in most other 

 species are more widely separated than the rest, and in the in- 

 terval the heart is usually placed. 



Another modification is seen in E. olivacea, PI. III. fig. 2; in 

 this species there are six pairs of branches, all of which are sim- 

 ple except the first or anterior pair ; these arise as usual from the 

 stomach, and are each divided into three branches. In E. de- 

 specta, PI. III. fig. 4, the arrangement is still more simplified : 

 after the branches of the first jiair come ofl^ in the ordinary way 

 from the stomach and pass on undivided, each to a single pa- 

 pilla, the central trunk passes to its termination in a zigzag di- 

 rection, giving oft' a branch at each angle to a large clavate pa- 

 pilla. There are in all four of these papillae on each side; they are 

 not in pairs however, but alternate. 



Other slight variations might be cited, but the above are the 

 chief modifications, and are perhaps sufficient to show to what 

 extent the digestive system varies in the genus Eolis. 



We have searched in vain for the lateral vessel described by 

 M. de Quatrefages, and have little hesitation in pronouncing its 

 non-existence in the genus. We have seen several species with 

 the ramifications coloui-ed, and in none of them have we observed 

 the slightest indications of such a vessel. In dissecting E. pa- 

 pillosa we made every endeavour to detect it, but \Ndthout success ; 

 and in a small specimen of that species we have since seen the 

 very terminations of the branches, and are quite satisfied that they 

 are isolated : the branches mostly ended in free blind sacs of va- 

 riable length ; others had their ends prolonged, bent outwards and 

 received into small papilla, which seemed to be in process of de- 

 velopment ; hence we inferred, that the glandidar apparatus in 

 the interior of the papillse was formed originally from the free 

 ends of the branches from the stomach, ^^'e are also of opinion 

 that when the animal is mature, the ends of all the branches will 

 be found to enter papillre. AVe have observed the termination of 

 branches in papilhe in a species which had their minute ramifi- 

 cations coloured : this species belongs to that portion of the ge- 

 nus of which E. coronata is the type. It is therefore probable 

 that M. de Quatrefages has been deceived by the doubling of the 

 skin at the sides of the body, caused by the pressui'c necessarily 

 used during the mode of investigation adopted by that gentle- 

 man : we have seen under such circumstances what might be 

 readily mistaken for a vessel. 



The prolongations of the branches from the gastric cavity that 

 arc continued into the papilla? are considerably modified in form 



