158 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



b. A thick layer of longitudinal muscular fibres (Fig. 

 90, b) between wliich numbers of small, nucleated cells 

 are scattered. 



c. The tubular bands; three longitudinal bands (Fig. 

 90, c) which lie in the muscular layer, on the dorsal side 

 of the nerve cord. 



d. The two ganglia (Fig. 89, d) which are imperfectly 

 separated from each other along the median line. Each 

 consists of : — 



1. A layer of large, granular, nucleated ganglion cells 

 (Fig. 89,/) which lie upon its ventral surface and sides. 



2. A central and dorsal non-transparent area {d) which 

 consists almost entirely of extremely fine intertwined 

 nerv^e fibres. 



e. The nerves (Fig. 90, g) which run ofi* on each side, 

 and consist of fine fibres like those in the dorsal portion 

 of the jjano^lion. 



g. The blood-vessels ; especially the large ventral ves- 

 sel (li) which runs along the body below the nervous 

 system. 



V. The Digestive Organs. 



a. In a section which passes through the pharynx, no- 

 tice : — 



1. The central cavity (/) which is reduced to a narrow 

 slit by the folding together of its walls. The form of this 

 slit varies greatly in sections from difierent parts of the 

 pharynx. 



2. A delicate layer of transparent cuticle, which lines 

 the cavity. 



3. The epithelium, formed by a single layer of large 

 nucleated cells. 



4. The very numerous blood-vessels, which lie just out- 

 side the layer of epithelium. 



