8l2 STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 



prominent papilla (u.g.} behind the anus. The dilated portions 

 of the two ducts are called by Hyrtl the horns of the bladder. 



The sides of the bladder and its so-called horns are pro- 

 vided with lateral pockets into which the collecting tubes of the 

 kidney open. These pockets, which we have found in two 

 female examples, are much larger in the horns of the bladder 

 than in the bladder itself. Similar pockets, but larger than 

 those we have found, have been described by Hyrtl in the male, 

 but are stated by him to be absent in the female. It is clear 

 from our examples that this is by no means always the case. 



Hyrtl states that the wide kidney ducts, of which his de- 

 scription differs in no material point from our own, suddenly 

 narrow in front, and, perforating the peritoneal lining, are con- 

 tinued forwards to supply the anterior part of the kidney. We 

 have already shewn that the anterior part of the kidney has no 

 existence, and the kidney ducts supplying it are, according to 

 our investigations, equally imaginary. 



It was first shewn by Miiller, whose observations on this point 

 have been confirmed by Hyrtl, &c., that the ovaries of Lepidosteus 

 are continuous with their ducts, forming in this respect an 

 exception to other Ganoids. 



In our example of Lepidosteus the ovaries (Plate 39, fig. 60, ov.) 

 were about 1 8 centims. in length. They have the form of simple 

 sacks, filled with ova, and attached about their middle to their 

 generative duct, and continued both backwards and forwards 

 from their attachment into a blind process. 



With reference to these sacks Miiller has pointed out and 

 the importance of this observation will become apparent when 

 we deal with the development that the ova are formed in the 

 thickness of the inner wall of the sack. We hope to shew that 

 the inner wall of the sack is alone equivalent to the genital ridge 

 of, for instance, the ovary of Scyllium. The outer aspect of 

 this wall i.e., that turned towards the interior of the sack is 

 equivalent to the outer aspect of the Elasmobranch genital ridge, 

 on which alone the ova are developed 1 . The sack into which 

 the ova fall is, as we shall shew in the embryological section, a 

 special section of the body-cavity shut off from the remainder, 



1 Treatise on Comparative Embryology, Vol. I., p. 43 [the original edition]. 



