OF PERIPATUS CAPEXSIS. 899 



Where the feet are given off the second transverse band be- 

 comes continuous with the main retractor muscular fibres in the 

 foot, which are inserted both on to the dorsal side and ventral 

 side. 



Muscular system of the feet. This consists of the retractors 

 of the feet connected with the outer transverse muscle and the 

 circular layer of muscles. In addition to these muscles there are 

 intrinsic transverse muscles which cross the cavity of the feet in 

 various directions (PI. 51, fig. 20). There is no special circular 

 layer of fibres. 



Histology of tJic muscle. The main muscles of the body are 

 unstriated and divided into fibres, each invested by a delicate 

 membrane. Between the membrane and muscle are scattered 

 nuclei, which are never found inside the muscle fibres. The 

 muscles attached to the jaws form an exception in that they are 

 distinctly transversely striated. 



THE BODY-CAVITY AND VASCULAR SYSTEM. 



The body-cavity, as already indicated, is formed of three 

 compartments one central and two lateral. The former is by 

 far the largest, and contains the alimentary tract, the generative 

 organs, and the mucous glands. It is lined by a delicate endo- 

 thelial layer, and is not divided into compartments nor traversed 

 by muscular fibres. 



The lateral divisions are much smaller than the central, and 

 are shut off from it by the inner transverse band of muscles. 

 They are almost entirely filled with the nerve-cord and salivary 

 gland in front and with the nerve-cord alone behind, and their 

 lumen is broken up by muscular bands. They further contain 

 the segmental organs which open into them. They are pro- 

 longed into the feet, as is the embryonic body-cavity of most 

 Arthropoda. 



The vascular system is usually stated to consist of a dorsal 

 heart. I find between the dorsal bands of longitudinal fibres 

 a vessel in a space shut off from the body-cavity by a con- 

 tinuation of the endothelial lining of the latter (fig. 16). The 

 vessel has definite walls and an endothelial lining, but I could 

 not make out whether the walls were muscular. The ventral 



