GOXADS 



425 



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 minute eggs and 



ti a-d 



int 



htpv s.inl.v 



e.ppor-1 f 



FIG. 1 10. Diasrram of the chief vessels of Ampliiorus. The arrows show the course 



taken by the blood. 



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

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

 branchial arteries ; kef>. port. v. hepatic portal vein ; hep. v. hepatic vein : in!. 

 intestine ; Ir. " liver " ; ph. pharynx ; s. int. r. 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.) 



sperms burst through into the 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 XIII. 



PRACT. ZOOL. 



E E" 



