ON THE DEVELOPMENT OP THE ELASMOBRANCH FISHES. 359 



middle line, dilated considerably, and commenced to exhibit 

 at their front ends the peculiarities of the adult. In the 

 male they are much less conspicuous, though still present. 



At the same time the tubules of the Wolffian body 

 become much more numerous, the Malpighian tufts appear, 

 and the ducts cease almost, if not entirely, to communicate 

 with the pleuro-peritoneal cavity. I have not made out 

 anything very definitely as to the development of the Mal- 

 pighian tufts, but I am inclined to believe that they arise 

 independently in the mesoblast of the intermediate cell mass. 



The facts which I have made out in reference to the deve- 

 lopment of the Wolffian duct, especially of its arising as a 

 series of involutions from the pleuro-peritoneal cavity, will be 

 found, I believe, of the greatest importance in understanding 

 the true constitution of the Wolffian body. To this I will 

 return directly, but I first wish to clear the ground by 

 insisting upon one preliminary point. 



From their development the Oviduct and Wolffian body ap- 

 pear to stand to each other in the relation of the Wolffian duct 

 being the equivalent to a series, so to speak, of Oviducts. 



I pointed out before that the mode of development of the 

 Oviduct could only be considered as a modification of a simple 

 involution from the pleuro-peritoneal cavity. Its develop- 

 ment, both in the Birds and in the Batrachians as an involu- 

 tion, still more conclusively proves the truth of this view. 



The explanation of its first appearing as a solid rod of 

 cells which keeps close to the epiblast is, I am inclined to 

 think, the following. Since the Oviduct had to grow a long 

 way backwards from its primitive point of involution, it was 

 clearly advantageous for it not to bore its way through the 

 mesoblast of the intermediate cell mass, but to pass between this 

 and the epiblast. This modification having been adopted, was 

 followed by the knob forming the origin of the duct coming to 

 be placed at the outside of the intermediate cell mass rather 

 than close to the pleuro-peritoneal cavity, a change which 

 necessitated the mode of development by an involution being 

 dropped and the solid mode of development substituted for 

 it, a lumen being only subsequently acquired. 



In support of the modification in the development being 

 due to this cause is the fact that in Birds the modes of 

 development of the Wolffian duct and the Oviduct are in- 

 verted. The Wolffian duct there arises diffierently from its 

 mode of development in all the lower vertebrates as a solid 

 rod close to the epiblast.' 



If the above explanation about the Oviduct be correct, 



1 if Romiti's observations ('Archives fiir Mikr. Anatom.,' vol. ix, p. 



