16 BRITISH PARASITIC COPEPODA. 



frontal and lateral margins give off seven pairs of 

 nerves. Three other pairs arise from the posterior- 

 end and form a sort of spinal cord. There are thir- 

 teen pairs of nerves altogether, as shown in Plate XV, 

 fig. 9. Each nerve, after leaving the main trunk, 

 sends out numerous branches which pass to the various 

 muscles controlling the appendages enervated by that 

 nerve. There is considerable difficulty in tracing the 

 endings of the branches when they pass amongst the 

 muscles. 



REPRODUCTION. 



The reproductive organs are paired, and as alivady 

 stated the sexes are distinct. In the mature female 

 the ovaries appear as comparatively large kidney- 

 shaped organs on each side of the anterior end of the 

 stomach. An oviduct arises near the anterior end of 

 the ventral surface and passes posteriorly as a narrow 

 tube until it enters the genital segment. It then 

 expands rapidly and becomes convoluted, finally pass- 

 ing out to the postero-lateral margins of the segment, 

 where it opens to the exterior just under the fifth feet. 

 Communicating with the oviduct near its extremity is 

 a short semi-transparent cement-gland which secretes 

 the enclosing membrane of the ovisac. The vulvae 

 are situated near the middle line close to the junction 

 of the genital segment with the abdomen. The vulva 

 appears to be a simple opening leading into the vagina 

 which expands into a receptaculum seminis. This is 

 an elongated sac passing from the median line to the 

 oviduct, which it enters alongside the duct of the 

 cement-gland. 



The sexual organs of the male are very similar in 

 position and arrangement to those of the female. 



