232 



ZOOLOGY 



SECT. 



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

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

 urinogenital 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 (kd. r ), so that, while resembling 



the rest of the organ in external appear- 

 ance, they do not discharge a renal 

 function. 



The male organs of Lepidosteus may 

 be taken as an example of those of 

 (ianoids. The testis (Fig. 907, 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 (l.c.) lying alongside the ureter (ur.). 

 From this canal tubes are given off which 

 communicate with the urinary tubules of 

 the kidney or open directly into the 

 ureter, so that the seminal fluid has to 

 traverse the latter 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. 876, v. d.) which unites with its 

 fellow of the opposite side and opens 

 either into a urinogenital sinus, as in the 

 Trout, or, as in the Cod, directly on the 

 exterior, between the anus and the urinary 

 aperture. In the Eels the seminal fluid 

 escapes into the ccelome and is discharged 

 by genital pores. 



In most Ganoids the oviducts (Fig. 908, 

 u 9 .a.p --w B, ovd.) have funnel-like anterior ends 



(ovd.") opening into the coelome, while 



FIG. 907. Male organs ol Lepi- V f 7 /\ ,1 v i 



dosteus. pi. bladder; i. c. posteriorly (ova. ) they discharge into the 



dilated ureters (bl.). A similar arrange- 

 ment occurs in the Smelt, one of the 

 Physostomi (Salmonidae), 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 Lepi- 

 dosteus (Fig. 908, 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 

 so pass directly into the oviduct without previously entering the 



61 



longitudinal canal ; tft. testis ; 

 ti.g. ap. urinogenital aperture ; 

 ur. ureter ; v. ef. vasa efferentia, 

 (After Balfour and Parker.) 



