BREATHING ORGANS IN OPISTIIOBRANCIIIATA 



159 



and HaJopsyclie are destitute of either, while the four remaining- 

 families have one branchia, sometimes lateral, sometimes posterior.^ 



Certain of the Nudibranchiata possess 

 no special breathing organs, and ])]"o- 

 bably respire through the skin {Elysia, 

 Limapontia, Cenia, Phyllirrhoe). The 

 majorit}', however, have developed see- 

 (jndai'y branchiae, in the form of promi- 

 nent lobes or leaf-like processes (the 

 ccrata), which are carried upon the back, 

 without any means of protection. These 

 cerata are, as a rule, of extreme lieauty 

 and variety of form, consisting sometimes 

 of long whip -like tentaculae, in other 

 cases of arborescent plumes of fern-like 

 leafage, in others of curious Ijead-like appendages of every imagin- 

 uljle shape and colour. In Doris they lie at the posterior end of the 



Fig. 66. — Valrata ■piscinalis 

 Miill. : hr, branchia ; Jl, fila- 

 ment ; f.I, foot loljL'>i. (Aftei- 

 Boutaii.) 





Fici. 67. — Doris (Arrliidons) 

 tuhercvlula L., Britain : a, 

 anus ; hr, branchiae, sur- 

 rounding tlie anus ; vi, male 

 organ ; rh, rh, rhinoi)liores. 

 xg. 



h- 



Fig. 68. — Pleiiroj)hyllidin h'ncata 

 Otto, Mediterranean : a, anus ; Itr, 

 secondary branchiae ; m, mouth ; 

 s.o, sexual orifice. 



body, in a sf)rt of rosette, which is generally capable of retraction 



into a chamber. In Fhyllidia and Pleuroyhyllidia these secondary 



branchiae lie, as in Fatella, on the lateral portions of the mantle. 



^ Pelseiieer, ' Cliallewjcr' Reports, vol. xxiii. part. l.wi. 



