46 W. A. HERDMAN. 



Tritoma. 



In Tritonia (e. g. Tritonia, or CandieUa, plebeia) the 

 body is long and low, nearly square in transverse section, and 

 tapers rapidly to the posterior end (fig. 13). The rhinophores 

 are large and complicated, having the base surrounded by a 

 sheath and the terminal part divided up into a number of 

 branches. There are no true branchiae such as are present iu 

 Doris and in Ancula, but placed along each side of the dorsal 

 surface is found a row of short branched cerata (fig, 13, c). 

 These are seen in sections (figs. 14 and 15) to be merely 

 processes of the body-wall containing no special structures and 

 only a few small lacunae, such as are present under the integu- 

 ment all over the body. In some transverse sections, where 

 the sides of the body are much corrugated the irregular folds 

 of the surface are almost as much branched as the cerata, and 

 have very much the same appearance (see k in fig. 14). 



It is clear then (1) that true branchiae, such as those of 

 Doris and Ancula, are not present in Tritonia plebeia; 

 (2) that the cerata of the latter are merely processes of the 

 body -wall like the cerata found along with branchiae in An c u 1 a ; 

 and (3) that although these cerata may become considerably 

 branched (see fig. 15) they have not the structure of special 

 respiratory organs. 



Dendronotus. 

 In Dendronotus arborescens there is practically the 

 same condition as in Tritonia. Branchiae are absent, but the 

 rhinophores are large and complicated, and the branched 

 cerata arranged along the sides of the back are so greatly de- 

 veloped as to form the most conspicuous part of the animal 

 in the living condition (PL VIII, fig. 16). There are usually 

 six pairs of these cerata, with occasional much smaller ones 

 scattered between. In a specimen 4 cm. in length the largest 

 pair of cerata may be 1 cm. iu height, and have stems 3 mm. 

 in diameter at the base. They branch repeatedly so as to form 

 an arborescent structure. 



