711 



MOLLUSCA OUTER ORGANISATION 



33 



and nephridial apertures lie on the right side of the body in front of 

 the anus. 



(b) Nudibranehia. The body is outwardly symmetrical, the 

 visceral dome does not protrude from it, but is closely applied to 

 the whole length of the foot, from which it is often not distinctly 



FIG. 43. Diagram of a Tectibranchiate Opistho- 

 branchiate. Lettering as before. In addition : gg, genital 

 ganglion ; s, shell ; <? , female genital aperture ; Ipp, rpp, 

 left and right parapodial lobes, that on the right laid back. 



FIG. 44. Dentalitun, diagram- 

 matic, left aspect, g, Sexual glands ; 

 M, cephalic tentacles ; other letter- 

 ing as before. 



differentiated. The foot has a flat creeping sole. There is no distinct 

 mantle fold, no gill corresponding with that of the Tectibranchia, 

 and no shell. The head carries tentacles or rhinophores, and sessile 

 eyes. The anus lies either dorsally in the median line, or laterally to 

 the right. The genital and renal apertures lie to the right in front 

 of the anus. The gills, which vary much in form, number, and 

 arrangement, are found dorsally or laterally, and are not homologous 

 with the typical Molluscan ctenidia. 



VOL. II 



