THE ANATOMY OF PENTASTOMUM TERETIUSCDLUM. 35 



appears to euter the^basal part of the hook^ and to swell out, 

 or at least to be in direct connection with a well-marked mass 

 of fibres (figs. 9, 10, 33, Hk. n.) with nuclei, which breaks up 

 into strands. The latter pass into connection with the cells 

 forming the layer beneath the cuticle, and at times appear to 

 pass right on to the cuticle itself. This fibrous structure is 

 very evident in all sections of the hooks, though it is difficult 

 to see what its meaning is, while in structure it has a some- 

 what close resemblance to that of the two nerve-cords which 

 pass along the ventral surface of the body (fig. 61). 



(6) This is one of two pairs of small nerves which arise 

 from the dorsal surface of the nerve mass. It runs directly 

 upwards behind the oesophagus to supply the walls of the mid- 

 gut. 



(7) This lies close behind the last mentioned, and runs in a 

 similar direction, passing into and supplying the hook-gland 

 by the side of the alimentary canal. 



(8) From the ventral surface arises posteriorly on each side 

 a small nerve which runs to the reproductive organs. In the 

 female it runs downwards and backwards, and passes on to 

 the walls of that portion of the organ where the duct from the 

 ovary on each side joins the short tube communicating with 

 the spermatheca, and from which arises the long coiled tube 

 which serves in the young form as a vagina, and in the mature 

 one as a uterus. 



In the male a sinoilar nerve runs almost directly down- 

 wards, and is distributed to the muscles concerned with the 

 cirrus sacs and the external opening. 



(9) The nerve mass is prolonged posteriorly into two large 

 cords which run backwards on the ventral side for nearly the 

 whole length of the body. 



In the female they pass between the two oviducts and sper- 

 mathecsBj and then turn downwards and enclose between them 

 the proximal part of the vagina, after which their course lies 

 ventral to the various organs in the body-cavity. 



In the male they pass backwards and downwards between 

 the two cirrus sacs, and then run along the body just above 



