XIII 



PHYLUM CHORDATA 



223 



size 



l.c 



ur- 



the pronephros usually atrophies. The ureter (ur.) is the 

 undivided segmental duct : it unites with its fellow of the opposite 

 side before opening either directly on to the exterior or into a 

 urine-genital sinus. A urinary bladder is formed as a single or 

 double dilatation of the ureter. The right and left kidneys undergo 

 more or less fusion, and their anterior 

 ends are usually converted into adenoid 

 or lymphatic tissue (ltd'.), so that, while 

 resembling the rest of the organ in ex- 

 ternal appearance, they do not discharge 

 a renal function. 



The male organs of Lepidosteus may 

 be taken as an example of those of 

 Ganoids. The testis (Fig. 846, ts.) is a 

 paired lobulated organ, the secretion of 

 which is carried by a large number of 

 vasa efferentia (v. ef.) into a longitudinal 

 canal (I. c.) lying alongside the ureter 

 (ur.). From this canal tubes are given 

 off which communicate with the urinary 

 tubules of the kidney, so that the 

 seminal fluid has to traverse these 

 tubules in order to reach the urinary 

 bladder (bl.) and make its escape by the 

 common urinogenital aperture (u.g. ap). 

 In Teleostei there are no vasa efferentia, 

 but the posterior end of the testis is 

 directly continued into a duct (Fig. 817, 

 v. d.) which unites with its fellow of the 

 opposite side and opens either into a 

 urino-genital sinus, as in the Trout, or, 

 as in the Cod, directly on to the exterior, 

 between the anus and the urinary aper- 

 ture. In the Eels the seminal fluid 

 escapes into the coelome and is dis- 

 charged by genital pores. 



In most Ganoids the oviducts (Fig. 

 847, B, ovd.) have funnel-like anterior 

 ends (ovd.") opening into the coelome, 

 while posteriorly (ovd/) they discharge 

 into the dilated ureters (bl.). A similar 

 arrangement occurs in the Smelt, one of the Phy sostomi, in which 

 the eggs are discharged from the outer or lateral face of the ovary 

 into the open end of the oviduct. But in most Teleostei and in 

 Lepidosteus (Fig. 847, A) the ovary (ovy.) is a hollow sac continued 

 posteriorly into the oviduct (ovd.) : the eggs are set free into its 

 cavity from the folds into which its inner surface is produced, and 



FIG. 84(3. Male organs of Lepi 

 dosteus. bl. bladder ; I. c. 

 longitudinal canal ; ts. testis ; 

 u.g. ap. urine-genital aperture ; 

 ur. ureter ; r. ef. vasa efferentia. 

 (After Balfour and Parker.) 



