358 F, M. BALFOUR. 



does not undergo important changes ; the hind end, however, 

 comes into connection with the extreme end of the ali- 

 meutary canal. The two Oviducts do not open together into 

 the cloaca, though, as my sections prove, their openings 

 are very close togetlier. The whole Oviduct, as might be 

 expected, shares in the general growth, and its lumen be- 

 comes in both sexes very considerably greater than it was 

 before. 



It is difficult to define the period at which I find these 

 changes accomplished without giving drawings of the whole 

 embryo. The stage is one considerably after the external 

 gills have appeared, but before the period at which the 

 growth of the olfactory bulbs renders the head of an elongated 

 shape. 



During the same period the Wolffian duct has undergone 

 most important changes. It has commenced to bud off 

 diverticula, which subsequently become the tubules of the 

 Wolffian body {vide fig. 13, w d). I am fairly satisfied that 

 the tubules are really budded off, and are not formed inde- 

 pendently in the mesoblast. The Dog-fish agrees so far with 

 Birds, where I have also no doubt the tubules of the Wolffian 

 body are formed as diverticula from the W^olffian duct. 



The Wolffian ducts have also become much longer than 

 the Oviduct, and are now found behind the anus, though 

 they do not extend as far forward as does the Oviduct. 



They have further acquired a communication with the 

 Oviduct, in the form of a narrow duct passing from each of 

 them into an Oviduct a short way before the latter opens 

 into the cloacal dilatation of the alimentary canal. 



The canals formed by the primitive involution leading from 

 the pleuro-peritoueal cavity into the Wolffian duct have 

 become much more elongated, and at the same time 

 narrower. One of these is shown in fig. 13, p, w d. 



Any doubt which could possibly be entertained as to the 

 true character of the ducts whose development I have de- 

 scribed is entirely removed by the development of the 

 tubules of the Wolffian body. In the still later stage than 

 this farther proofs are furnished involving the function of 

 the Oviduct. At the period when the olfactory lobes have 

 become so developed as to render the head of the typical 

 elongated shape of the adult, I find that the males and 

 females can be distinguished by the presence in the former 

 of the clasping appendages.^ I find at this stage that in the 

 female the front ends of the Oviducts have approached the 



I For tLe specimens of this age I am indebted to Professor Huxley. 



