STRUOTUEE, ETC., OP CERATA OE NUDIBRANCHS. 53 



way along. In (?) Cutliona nana (figs. 36, 37) the sac is 

 short and rounded, and the cnida are much smaller than in the 

 last species, but still spherical in form ; while in Galvina 

 pi eta (figs. 31, 32) the sac is more elongated, the cnidocysts 

 are very distinct (fig. 40), and the cnida are narrow rod-like 

 bodies (fig. 33). 



The hepatic cseca occupying the greater part of the interior 

 of the cerata (see figs. 34 and 35, which show transverse sections 

 of two species) reach nearly or quite to the lower end of the 

 cnidophorous sac, and communicate with it by means of a 

 longer or shorter slender tube with thin walls strengthened 

 by a few muscle-fibres. In Facelina drummondi (figs. 

 28 and 30) the connecting-tube is very long, and may be bent 

 upon itself. In the small species of Eolis shown in figs. 36 

 and 37 (probably Cuthona nana) the cnidophorous sac is 

 nearly spherical, and the connecting-tube is short and has a 

 distinct muscular thickening, forming a sphincter around the 

 small opening into the hepatic caecum. This condition suggests 

 that possibly in all cases the communication between the 

 hepatic caecum and the exterior through the cnidophorous sac 

 may not be permanently open, but be kept closed when required 

 by the contraction of the sphincter muscle. 



Functions of the Cerata. 



In regard to the functions of these various kinds of cerata 

 in the Nudibranchiata, in the first place I do not think that in 

 any case they are specially branchial. In Ancula, as I have 

 shown above, there are parieto-cerata existing along with true 

 branchiae, and the two have a distinct structure, so that, 

 although in sections pieces of the cerata and of the branchiae 

 may become displaced, they can be distinguished by their 

 structure from one another. Then in Tritonia and in 

 Dendronotus 1 have shown that the parieto-cerata agree in 

 structure with those of Ancula, and not with the true 

 branchiae of Doris and Ancula. From a recent conversation 

 with Dr. Bergh I learn that he regards the cerata as having a 

 branchial function, and even in Ancula, where there are 



