XI 



PHYLUM MOLLUSCA 



305 



of different hues are to be noticed passing over the surface. 

 These are due to the presence of numerous contractile 

 pigment-containing cells or chromatophores (Fig. 177), which 

 contract and expand under nervous influence and are situated 

 in the deeper layers of the integument over the entire surface. 

 On the postero-ventral aspect of the body, the mantle 

 encloses a wide cavity, the mantle-cavity (Figs. 178, 179), 



FIG. 179. Nautilus pompilius, interior of mantle cavity of a male specimen with 

 the postero-ventral wall reflected, a. I. neph. ap. oral left nephridial aperture ; 

 an. anus ; cten. ctenidia ; /. 6" ap. left reproductive aperture ; /. ant. os. left oral 

 osphradium ; /. vise. ap. left viscero-pericardial aperture ; want, flaps of mantle ; 

 pen. penis ; p. 1. neph. ap. aboral left nephridial aperture ; p. r. neph. ap. aboral 

 right nephridial aperture ; post. os. aboral osphradia ; r. vise. ap. right viscero- 

 pericardial aperture. 



in which the ctenidia are lodged, and on the wall of which 

 are situated the anal, excretory and reproductive apertures. 

 The mantle-cavity communicates at its oral end by a wide 

 slit with the exterior ; but this is capable of being closed, 

 so that when the walls of the cavity contract, a stream of 

 water is ejected through the funnel, and the animal is 

 Man. Zool. X 



