36 Dr. C. Collingwood on some points in the Economy 



Mollusks collectively which appeared to possess it, the terra 

 " Phlebentcrata." M. Milne-Edwards, however, subsequently 

 abandoned this theory, owing to the discoveries and arguments 

 of M. Souleyet in France, and Messrs. Hancock and Embleton 

 in England, all of whom maintained that the so-called gastro- 

 vascular apparatus was no other than a highly developed system 

 of biliary ducts in connexion with a divided liver. And the 

 result of the controversy between these eminent anatomists was, 

 that instead of it being proved that the Nudibranchiata exhi- 

 bited in their structure a degi'adation of type, as had been main- 

 tained by Quatrefages, it was demonstrated by Messrs. Hancock 

 and Embleton that in Doris, at least, a portal heart existed, and 

 that all the Nudibranchiata possessed a sympathetic system of 

 nerves, being the first instance in which they had been fully 

 proved to exist in the Invertebrata, and a remarkable example 

 of the value of controversy, such as is often aroused by erroneous 

 statements. 



The learned authors of the Ray Society's Monograph, how- 

 ever, distinctly affirm that, "from the state of the circulatory 

 apparatus, the respiration is performed 07ihj in part by the 

 branchipe,'' and further that " in all the families, the skin, which 

 is covered with vibratile cilia, acts as an imperfect accessory 

 breathing organ." And considering these statements, we can 

 scarcely regard the term Nudibranchiata as anything but a mis- 

 nomer, or, at all events, only to a limited extent correct. In 

 the instance before us, the branchiee were absent, and yet the 

 animal was lively. Mr. Alder suggested that the branchiae might 

 have been decomposed ; but special inquiry of my correspondent 

 who dredged it, elicited the fact that he looked for branchiae, 

 but saw none. How long this little animal may have existed 

 without these appendages we cannot say, but it cannot have 

 been less than three days ; and yet it belonged to a family in 

 which the branchiae are considered to attain a high degree of 

 development, and may therefore be supposed to have more of the 

 work of aeration to perform. 



So also in the genus Eolis, the papillae or branchiae (so called) 

 generally begin to fall off before the animal dies ; and I have 

 seen specimens of E. Drummondi crawling about with their 

 backs entirely bare. Whether this may prove anything agamst 

 their value as breathing organs may be considered doubtful; 

 for even supposing them to be gastro-hepatic organs, the loss 

 of any, or at all events of most of them, should, a priori, be 

 fatal. 



Mr. Lewes says he has seen food oscillating in the papillae of 

 Eolis, simultaneously with the ordinary locomotive movements 

 of the body ; and when we consider the universal morphologies 



