12 



COMPARATIVE ANATOMY 



CHAP. 



at its anterior end. No jaws. The anus almost always dorsal. Except in the 

 Steganobranchia, the disappearance of the mantle and its cavity is accompanied by 

 the disappearance of the single ctenidium of the Tectibranchia. 



Section 1. Steganobranchia. With mantle, cavity, and ctenidium to the right ; 

 with a shell and parapodia. Fam. Oxynoidea (Oxynoe, Lobiger}. 



Section 2. Cirrobranchia. Leaf- or club-shaped processes found laterally on the 

 back. Fam. Hermseidse, Phyllobranchidse. 



Section 3. Pterobranchia. The sides of the body produced into lobes, in 

 which the branches of the glands of the mid -gut spread out. Fam. Elysiadse, 

 Placobranchidse. 



Section 4. Abranchia. Neither ctenidium, nor dorsal appendages, nor leaf-like 

 lateral expansions of the body. Respiration through the skin. The body is almost 

 like that of a Planarian. Fam. Limapontiidae. 



Sub-Order 3. Nudibranchia. 

 Without mantle fold, shell, or ctenidium. Jaws almost always found. Radula 



FIG. IS. Aeolis rufibranchialis (right aspect, after Alder and Hancock), a, Eye ; 6, oral 

 tentacle ; c, cephalic tentacle ; d, anus ; e, genital aperture ; /, dorsal respiratory appendages 

 (cerata). 



generally well developed, with teeth which fall off and are lost*. Adaptive gills 

 very variously developed, but occasionally wanting. 



V 



11 12 



FIG. 19. Phyllirhoe bucephalum (lateral aspect, after Souleyet, modified). 1, Tentacle; 

 2, cerebral ganglion ; 3, stomach ; 4 and 12, intestinal cseca (forming the" digestive gland) ; 

 5 ventricle ; 6, auricle ; 7, pericardial aperture of the kidney ; 8 kidney ; 9, external aperture of 

 the same (on the right side) ; 10, anus (on the right side) ; 11, hermaphrodite glands, the ducts not 

 drawn ; 13, genital apertures ; 14, buccal ganglion ; 15, salivary glands. 



Section 1. Holohepatica. One large unbranched hepatic gland (liver). Fam. 



