152 



PISCES. 



Generative Organs. The animals are dioecious. The ovaries and 

 testes resemble each other externally, and consist of a series of 

 paired bodies. They are arranged segmentally (in prolongations of 

 the body cavity), one pair being found in each segment over the 



D =F 



Oe 







BL 



D' 



Kl 



FIG. 598. Development of Amphioxiis (after B. Hatschek). A, Blastosphere. B, commencing 

 invagination of the entoclerm (gastrula). C, Later gastrula, the cilia of the ectoderm 

 cells are not represented. D, Stage with two somites (primitive segments), seen in 

 optical longitudinal section. US, Primitive segments or somites ; MF, mesoderm folds , 

 N, medullary canal ; Oe, external opening of the latter. E, Stage with nine somites 

 seen from the dorsal surface to shew the asymmetry of the somites, the notochord (Ch) 

 is shown in section. F, Larva with mouth (O) and first gill slit (K) seen from the left 

 side; D, intestine ; SI, ventral blood-vessel. 



greater part of the length of the branchial sac (fig. 597, Ov). The 

 generative products are dehisced into the atrial cavity, and pass 

 thence through the pharynx and mouth to the exterior. 



For a short distance in front of the atrial pore the epithelium of 



