GONADS 



409 



end is a ciliated depression usually known as the olfactory 

 pit {plf. p). There is no auditory organ. The dorsal and 

 ventral nerves (Fig. 100 A, sn) remain separate, and do 

 not unite to form a nerve-trunk (compare p. 163). 



The sexes are distinct, and the metamerically arranged 

 gonads (Fig. 98-100, gon. g) are situated in pouches, the 

 cavities of which represent part of the coelome and which 

 project into the atrium on either side of the pharynx. When 



t.f.iirm tji 



£L a.o ,.^ 



qf.br.a- ""o-o ^.f^ra. '■'• 



Fk;. ioi. — Diagram of the vascular .system oi Ainphioxtis. - ■ 

 a/.br.a. afferent branchial arteries; /'r. tV. gill-slits ; cp. interstinal capillaries; 

 d. ao. paired dorsal aortEe ; d. ao'. median dorsal aorta ; ef. bj: a. efferent 

 branchial arteries ; kep. port, v. hepatic portal vein ; hep. v. hepatic vein ; int. 

 intestine ; Ir. liver ; ph. pharynx : s. int. v. sub-intestinal \'ein ; v. ao. ventra 

 aorta. (From Parker and Haswell's Z(7£>/cj^j.) 



ripe, the eggs and sperms are shed into the atrium and find 

 their way out through the atriopore. 



The oosperm undergoes segmentation, and gives rise to a 

 simple larva., which gradually develops into the adult form. 

 The embryology of Amphioxus, which is very instructive, 

 will be referred to in greater detail in Chapter XL 



