lOG SEA-SIDE STUDIES. 



and biliary apparatus ; but you see nothing to warrant the 

 accepted notion tluit they are respiratory organs. I certainly 

 saw nothing of the kind. It was a doubt which early forced 

 itself upon me. Zoologists class the Eolis among Nudi- 

 branchiates, but I could detect nothing like a gill in these 

 said naked-gilled molluscs ; and a series of dissections served 

 to transform doubt into a conviction, and satisfactorily proved 

 the term " branchial papillse " to be altogether erroneous. 

 These papillae have neither the specific structure, nor the 

 anatomical connection of gills. Various as gills are, they 

 have uniformly a system of vessels carrying the blood to 

 them for aeration, and a system of vessels carrying the 

 aerated blood from them. Have the papillae of the Eolis such 

 vessels ? Nothing of the kind. The blood they receive, which 

 is not more than other parts of the body, is received into 

 sinuses, as it is in the peritoneal cavities ; and it is not more 

 aerated there than it is in every other part of the mantle 

 from which the papillse rise. If, therefore, we can detect in 

 these papillae neither the ordinary structure of gills, nor the 

 vessels which carry blood to and from gills, it is eminently 

 unphilosophic to call them giUs, and to class the Eolids among 

 Nudibranchiates. 



Do but examine one of the other Nudibranchiates — say a 

 Doris — and you will there find the very characteristics want- 

 ing in the Eolis. It has a gill, distinct, unmistakable; 

 although even here the gill performs but a small part in the 

 aeration of the whole blood. According to Alder and 

 Hancock, only that portion of the blood which sui)plies the 

 liver-mass goes to the gill ; but small as the part may be, 



