246 MR. NEWPORT ON THE IMPREGNATION OF THE OVUM IN THE AMPHIBIA 



6. TESTS OF FECUNDATION. 



I have given some account in my former paper* of a space, or chamber, which is 

 developed between the vitellary envelope of the egg and the upper surface of the yelk, 

 within the first hour and a half, subsequent to the encounter of the spermatozoon with 

 the egg ; and I have referred to it in the details of these experiments, as occurring in 

 some of the eggs which had been immersed during twenty-five minutes before the 

 fecundatory agent was supplied to them, and as marking their having been affected 

 by its influence. The formation of this chamber is one of the earliest and most cer- 

 tain indications that the egg has been more or less impregnated. The earliest 

 symptom of impregnation occurs somewhat sooner than the formation of the chamber, 

 or within the first half-hour, and consists in a marked increase in the degree of undu- 

 latory heaving and sinking of portions of the surface of the yelk, motions which take 

 place slightly in the unirnpregnated egg, but are increased in the impregnated; 

 although, even in that, they are not sufficiently permanent to be easily recognized as 

 proofs of fecundation. The irregular contraction and shrivelled appearance of the 

 yelks, noticed in the preceding observations, may, perhaps, be due in part to this 

 cause. The formation of the chamber is the result of the contraction and depression 

 of the upper surface of the yelk, occasioned, as there is reason to think, by changes 

 which are going on within the substance of the upper hemisphere of the yelk, around 

 the embryo vesicle, or its progeny, and which changes appear to be due to the opera- 

 tion of the spermatozoon ; as I have never observed the chamber in any egg which 

 has not been more or less fecundated. The fact of the existence of a chamber, therefore, 

 may always be regarded as a. proof of fecundation. It is commenced sooner or later 

 according to the temperature of the surrounding medium, and to the more or less 

 complete fecundation of the egg. It is usually perceptible in about one hour, or one 

 hour and a quarter after the impregnating fluid has been supplied to the egg, and is 

 distinctly marked in less than one hour and a half, when the eggs are preserved in a 

 temperature of from 50 to 55 FAHR., and its size is increased during the first three 

 hours. It is commenced in a slight depression in the centre of the upper surface of 

 the yelk, at a point which corresponds to the entrance to the central canal, and it 

 takes place much sooner in eggs which have been completely fecundated, even at 

 moderate temperatures, than in others which have been more sparingly affected. I 

 have seen it begun in a fully impregnated egg, in a temperature of 52 FAHR., at fifty- 

 three minutes after encounter with very mature spermatozoa. When it has attained its 

 greatest superficial extent it appears like a clear watch-glass cavity, filled with a per- 

 fectly transparent, limpid fluid above the dark upper surface of the egg. After the 

 third hour it becomes slightly further enlarged in its axis from above downwards by 

 the formation of a shallow, funnel-shaped depression on the surface of the yelk, the 

 centre of which is the minute orifice seen by PREVOST and DUMAS, and BAKU, and this 

 is continuous with the canal above alluded to. I have never found this chamber 



* Philosophical Transactions, 1851, p. 187. 



