EXPLANATION OF PLATE 39. xlix 



Fig. 52. Transverse section through the region of the stomach of an embryo 

 1 5 millims. in length, shortly after hatching, to shew the glomerulus and peritoneal 

 funnel of pronephros. 



Fig. 53- Transverse section through posterior part of the body of an embryo, 

 about a month after hatching, shewing the structure of the mesonephros, the spiral 

 valve, &c. 



PLATE 39. 



Figs. 54, 55, 56, and 57 are a series of transverse sections through the genital 

 ridge and mesonephros of one side from a larva of 1 1 centims. 



Fig. 54. Section of the lymphatic organ which lies in front of the mesone- 

 phros. 



Fig- 55- Section near the anterior end of the mesonephros, where the 

 genital sack is completely formed. 



Fig. 56. Section somewhat further back, shewing the mode of formation of 

 the genital sack. 



Fig- 57- Section posterior to the above, the formation of the genital sack not 

 having commenced, and the genital ridge with primitive ger- 

 minal cells projecting freely into the body-cavity. 



Fig. 58 A. View of the testis, mesorchium, and duct of the kidney of the left side 

 of an adult male example of Lepidosteus, 60 centims. in length, shewing the vasa 

 efferentia and the longitudinal canal at the base of the mesorchium. The kidney 

 ducts have been cut open posteriorly to shew the structure of the interior. 



Fig. 58 B. Inner aspect of the posterior lobe of the testis from the same example, 

 to shew the vasa efferentia forming a network on the face of the testis. 



Figs- 59 A and B. Two sections shewing the structure and relations of the 

 efferent ducts of the testis in the same example. 



Fig. 59 A. Section through the inner aspect of a portion of the testis and 

 mesorchium, to shew the network of the vasa efferentia (n v e) 

 becoming continuous with the seminal tubes (si). The granu- 

 lar matter nearly rilling the vasa efferentia and the seminal 

 tubes represent the spermatozoa. 



Fig. 59 B. Section through part of the kidney and its duct and the longitu- 

 dinal canal (Ic) at the base of the mesorchium. Canals (s c) 

 are seen passing off from the latter, which enter the kidney and 

 join the uriniferous tubuli. Some of the latter (as well as the 

 seminal tubes) are seen to be filled with granular matter, 

 which we believe to be the remains of spermatozoa. 



Fig. 60. Diagram of the urinogenital organs of the left side of an adult female 

 example of Lepidosteus 100 centims. in length. This figure shews the oviduct (od) 

 continuous with the investment of the ovary, opening at od' into the dilated part of 

 the kidney duct (segmental duct). It also shews the segmental duct and the junction 

 of the latter with its fellow of the right side to form the so-called bladder, this part 

 being represented as cut open. The kidney (/') and lymphatic organ (ly) in front of it 

 are also shewn. 



