STETJOTURB, ETC., OF CERATA OF NUDIBRANCHS. 41 



On the Structure and Functions of the Cerata 

 or Dorsal Papillae in some Nudibranchiate 

 MoUusca. 



By 



^T. A. Herdman, D.Sc, F.Ii.S., 

 Professor of Natural History in University College, Liverpool. 



With Plates VI, VII, VIII, IX, and X. 



Most of the Nudibranchiate Mollusca are provided with 

 brightly coloured and sometimes elaborately branched projec- 

 tions from the sides and dorsal surface of the body. These 

 include — 



1. The Rhinophores, or dorsal tentacles. 



2. The true Branchiae. 



3. The Cerata^ or dorsal papillse. 



The rhinophores are a pair of tentacles placed near the 

 anterior end of the body^ on the dorsal surface of the head. 

 They are undoubtedly sense-organs^ and are supplied by large 

 nerves arising from the cerebral ganglia. They are present in 

 all the forms discussed in this paper. 



The branchiae, although they may possibly not be true 

 ctenidia, are specialised organs of respiration. They are not 

 present in all Nudibranchs. 



The cerata, which were the special subject of my investiga- 

 tion, vary greatly in number, size, and arrangement in the 

 different genera and species, and the characteristic appearance 

 of the animals is in a great measure due to these structures. 

 They are often termed dorsal papillse, or branchial papillae, or 

 even branchiae ; and they have been supposed by many zoo- 



