\l 



PHYLUM ARTIIROPODA 



.-,:;: 



canal from the water-sac beneath the cuticle of the paired 



eyes. 



Reproductive Organs. — The large majority of individuals 

 both of Apus and Lepidurus are females ; males are of com- 

 paratively rare occurrence. The ovary (Fig. 424, ovy.) is a branched 

 tube occupying a considerable portion of the body-cavity in 

 sexually mature individuals. The walls of the tube arc lined 

 with epithelium, and give rise to ova, which pass into the lumen 

 of the tube and thence to a duct (ovd.) opening on the eleventh or 



Fio. 428. — Diagram of two ommatidia from the paired eyes of Apus. cc. vitreous cells ; rr. vit- 

 reous body ; H. connective-tissue fibre; Inj. epiderm cells; p. pigment cells; ;•, inner parts 

 of ommatidia ; re. rctiuula; ; rh. rbabdomc. (From Bernard.). 



last thoracic segment. As in Leeches (p. 515), there is reason 

 for thinking that the cavity of the ovarian tube represents a 

 shut-off portion of the coelomc, and the oviduct a nephridium. 

 One species has been shown to be hermaphrodite : in others 

 males are occasionally found, but reproduction appears to be, as a 

 rule, parthenogenetic. 



Development. — The eggs are centrolectthcU, i.e., have an 

 accumulation of yolk in the centre surrounded by a superficial 

 layer of protoplasm. The process of segmentation and the forma- 

 tion of the germ-layers have not been observed. 



