180 MR. NEWPORT ON THE IMPREGNATION OF 



of the Frog about three hours after impregnation (fig. 10 a), but have not traced 

 them to their origin. With regard to the disappearance of the spot in the germinal 

 vesicle, the facts observed in the ova of the Frog agree with those noticed by KOL- 

 LIKER* in the ova of intestinal worms, that all appearance of the spot is lost before 

 that of the vesicle. This circumstance, however, may be owing either to the spot 

 having given origin to cells in the vesicle which quickly attain to similar dimensions, 

 and from which it is not otherwise distinguished ; or to its becoming entirely obscured 

 by their multiplication. Although no observations have been made on the origin of 

 the embryo vesicle that appears in the yelk after the disappearance of the germinal, 

 I am still inclined to regard this as being in some way derived from the lost germinal 

 spot, notwithstanding that KOLLIKER found a certain period of time elapse between the 

 disappearance of the vesicle and that at which he was able to recognize this body. 



Transit of the Ovum. Thus, then, when the ovum escapes from the ovisac and 

 ovary into the cavity of the abdomen, the germinal vesicle and spot have entirely 

 disappeared, and it consists only of the yelk enclosed in an exceedingly delicate, struc- 

 tureless, vitelline membrane. This is its condition in the Frog, Toad and Newts. It 

 is then extremely delicate and easily lacerated. The mode in which the ovum passes 

 into the oviduct has been the subject of much inquiry. I am quite certain, as SWAM- 

 MERDAM long ago showed, that the ova, when mature, pass from the ovaries into the 

 cavity of the abdomen, and from thence into the oviducts, in the Frogs, Toads and 

 Newts, quite independent of any intercourse with the male, as I have myself recently 

 had an opportunity of proving. The frog I have already mentioned (p. 173.) as 

 having watched through its season of hybernation, was kept apart from all others 

 until the 2nd of April, at which time she had not deposited any ova. But from the 

 altered form of her body it was evident that the ova had passed, or were at that time 

 in the act of passing, into the oviducts. I then placed her in a vessel with others, 

 some of which were males, but not one of these joined with her. Nevertheless, on 

 the 6th of April she cast her ova, without having paired, and died on the following 

 day. On examination after death, I found that the whole of the ova had left the 

 ovaries, all of which, excepting only two still free in the cavity of the abdomen, had 

 passed through the oviducts without any intercourse with the male. These ova of 

 course were sterile, but it was worthy of note that their envelopes did not expand to 

 so great an extent as those of the eggs of paired individuals. 



Passage into the Oviduct. In what way the ova pass from the cavity of the abdomen 

 into the mouth of the duct has never been satisfactorily explained. SWAMMERDAM 

 examined the question with much care-f-, but was unable to form any decided opinion 

 respecting it, as he correctly states that the mouths of the ducts are at a distance 

 from the ovaries, and are not free to grasp the ova like the fimbriated extremities of 

 the Fallopian tubes in Mammalia, but are confined in the peritonaeum, which is con- 

 tinuous with that which passes over the pericardium and heart. PREVOST and DUMAS 



* MULLER'S Archiv, 1843. t Book of Nature, part 2, pp. 108, 109. 



