180 INVERTEBRATE ANIMALS. 
of most Molluscs, the “foot,” and is therefore called the 
“pedal” ganglion. The third is known by the cumbrous name 
of the “ parieto-splanchnic” ganglion, because it supplies ner- 
vous filaments to the walls (farietes} of the body, and also to 
the internal organs (sp/anchna). In all the higher Molluscs it 
is this scattered condition of the nervous masses which distin- 
guishes them so sharply from all other animals. Distinct re- 
spiratory organs may or may not be present, and they may 
be adapted for breathing air directly or through the medium 
of water. All the higher Aod/usca are simple animals, and 
Fig. 94.—Diagrammatic section of aWhelk. @ Mouth, with masticatory apparatus; 
6 Salivary glands ; c Stomach ; @d Intestine, surrounded by the liver, and ter- 
minating in the anus (e) ; g Gill ; 2 Heart ; f Nervous ganglion. 
perpetuate their kind by means of the sexes, but many of the 
lower forms have the power of producing colonies by continu- 
ous gemmation, much as we have formerly seen in the Hydroid 
Zoophytes. 
The digestive system in all the M/o//usca consists of a mouth, 
gullet, stomach, intestine, and anus (fig. 94), with the exception 
of a few forms in which the intestine ends blindly. In some the 
mouth is surrounded by ciliated tentacles (Polyzoa, fig. 96) ; in 
others it is furnished with two long ciliated arms (Brachiopoda, 
