STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 825 



urinary bladder, Hyrtl). These relations seem to prove beyond 

 a doubt that the oviduct of Lepidostens is for its major part 

 homologous with the genital ducts of other Ganoids. 



The relationship of the genital ducts to the kidney ducts in 

 Amia and Polypterus is somewhat different from that in the 

 Chondrostei and Lcpidosteus. In Amia the ureters are so small 

 that they may be described rather as joining the coalesced 

 genital ducts than vice versa, although the apparent coalesced 

 portion of the genital ducts is shewn to be really part of the 

 kidney ducts by receiving the secretion of a number of meso- 

 nephric tubuli. In Polypterus the two ureters are stated to 

 unite, and open by a common orifice into a sinus formed by the 

 junction of the two genital ducts, which has not been described 

 as receiving directly the secretion of any part of the meso- 

 nephros. 



It has been usual to assume that the genital ducts of Ganoids 

 are true Miillerian ducts in the sense above defined, on the 

 ground that they are provided with a peritoneal opening and 

 that they are united behind with the kidney ducts. In the 

 absence of ontological evidence this identification is necessarily 

 provisional. On the assumption that it is correct we should 

 have to accept the second of the two alternatives above sug- 

 gested as to the development of the posterior parts of the oviduct 

 in Lepidostens. 



There appear to us, however, to be sufficiently serious objec- 

 tions to this view to render it necessary for us to suspend our 

 judgment with reference to this point. In the first place, if the 

 view that the genital ducts are Mullerian ducts is correct, the 

 true genital ducts of Lepidosteus must necessarily be developed 

 at a later period than the secondary attachment between their 

 open mouths and the genital folds, which would, to say the least 

 of it, be a remarkable inversion of the natural order of develop- 

 ment. Secondly, the condition of our oldest larva shews that 

 the Mullerian duct, if developed later, is only split off from quite 

 the posterior part of the segmental duct ; yet in all types in 

 which the development of the Mullerian duct has been followed, 

 its anterior extremity, with the abdominal opening, is split off 

 from either the foremost or nearly the foremost part of the seg- 

 mental duct. 



B- 53 



