GONADS 



425 



1'here is no auditory organ. The dorsal and ventral nerves 

 (Fig. 109 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 (Figs. 106, 107, and 109 A, 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 ripe, the eggs and sperms burst through 



d.CLO &&r.a. <t 



d CLO 



e.pporl.1/ 



FIG. no. Diagram of the chief vessels of A mphiox u s. The arrows show the course 



taken by the blood. 



of. br. a, afferent branchial arteries ; br. cl. gill-slits ; cp. intestinal capillaries ; 

 d. ao. paired dorsal aortae ; d. ao . median dorsal aorta ; ef. br. a efferent 

 branchial arteries ; hep. port. i>. hepatic portal vein ; hep. v. hepatic vein ; int. 

 intestine ; Ir. " liver" ; ph. pharynx : .y. int. v. sub-intestinal vein ; v. ao. ventral 

 aorta, which contracts from behind forwards. (Representatives of the precaval 

 and cardinal veins of fishes are also said to be present.) (From Parker and 

 Haswell's Zoology.") 







into fhe atrium and find their way out through the atriopore. 

 The oosperm undergoes segmentation, and the embryo 

 is hatched at a relatively early stage as 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 XII. 



