54 W. A. HER DM AN. 



large true branchiae present^ he thinks that the cerata are 

 supplementary respiratory organs. I am still of opinion, how- 

 ever, that, considering the relatively large size of the branchise 

 and the perfection of their adaptation to their function and 

 the absence of any such adaptation in the cerata, the action 

 of the latter in effecting respiration must be so feeble, com- 

 pared with the action of the branchiae, that it may be neglected. 

 Dendronotus arborescens is the form in which it might 

 be most readily supposed that the parieto- cerata have ac- 

 quired, secondarily, a branchial function, but a close com- 

 parison of sections shows that these processes do not contain 

 more blood-cavities than the general body-wall, and have not 

 even so many small lacunae close to the surface as some parts 

 of the dorsal and lateral integument. Hence, although they 

 may by their extended surface aid somewhat in respira- 

 tion, still they cannot be regarded as in any way specialised 

 branchiae. 



Then, again, in Eolis and Doto, although from their 

 relatively very large size the hepato-cerata may be of some 

 importance in respiration, it is merely as being an extension of 

 the general integument, and not as being special respiratory 

 organs. Nearly the whole of the space in the hepato-cerata 

 in these two genera is occupied by the large hepatic caeca, and 

 there are only a few small blood-lacunae to be seen scattered 

 here and there in sections. Specimens of both Eolis and 

 Doto continue to live after being deprived of most of their 

 cerata; so, both from their constitution and as the result of 

 experiment, it may be inferred that these structures cannot be 

 of primary importance as respiratory organs. One function, 

 of course, of the cerata in these genera is to contain the greater 

 part of the liver ; and no doubt this has led to an increased 

 size and some modification of structure. In Eolis, finally, the 

 apices of the hepato-cerata accommodate the cnidophorous 

 sacs, which act, doubtless, as important organs of off'ence. 



But I believe that, in addition to these minor functions, the 

 cerata of the Nudibranchiata are of primary importance in 

 giving to the animals, by their varied shapes and colours. 



