BREATHING ORGANS IN OPISTHOBRANCHIATA 



59 



both lateral and posterior branchiae well developed, Clione and 

 Halopsyche are destitute of either, while the four remaining fam- 

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



Certain of the Nudibranchiata possess 

 no special breathing organs, and prob- fl 

 ably respire through the skin (^Elysia, 

 Limaj)ontia^ Cenia^ Phyllirrhoe) . The 

 majority, however, have developed sec- 

 ondary branchiae, in the form of promi- 

 nent lobes or leaf-like processes (the 

 cerata)^ which are carried upon the back, 

 without any means of protection. These 

 cerata are, as a rule, of extreme beauty 

 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 bead-like appendages of every imaginable 

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



Fig. &Q. — Valvata pisciualis 

 Miill, ; br, branchia ; fi, 

 filament; f.l, foot lobes. 

 (After Boutan.) 



Fig. 67. — Doris (Archidoris) 

 tuberculata L., Britain: a, 

 anus; br, branchiae, sur- 

 rounding the anus; m, male 

 organ; rh, rh, rhinophores. 



^r. 



Fig. 68. — Pleurophyllidia lineata 

 Otto, Mediterranean : a, anus ; br, 

 secondary branchiae ; to, mouth ; 

 s.o, sexual orifice. 



body, in a sort of rosette, which is generally capable of retraction 



into a chamber. In Phyllidia 'aradi Pleurophyllidia these secondary 



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



1 Pelseneer, ^Challenger'' Beports, vol. xxiii. part Ixvi. 



