198 MR. NEWPORT ON THE IMPREGNATION OF 



the removal from low to high temperature was within the first half hour ; while it did 

 not occur, in the only experiment in which it happened in Set F, No. 1, until the end 

 of sLr hours and a-half, when the removal from a similar low to a like high tempera- 

 ture was not made until one hour and a half after impregnation. 



The influence of temperature is thus as marked in its effects on the impregnation 

 of the ovum as it can be proved to be on the future development of the embryo. 

 Impregnation is accelerated, and also is more certain in its occurrence in a high 

 than in a low temperature. In the latter it becomes retarded and is less determined. 

 This applies equally to the susceptibility of the ovum, and to the fitness of the im- 

 pregnating fluid to effect impregnation. But in proportion as this fitness is exalted 

 by increase of temperature, so is the duration of the capability to receive in the one, 

 and the efficiency to communicate in the other diminished. SPALLANZANI found that 

 the ova of toads placed in an ice-house could be impregnated at the end of forty-one 

 hours*. PREVOST and DUMAS -J- also mention that they were successful, and that too 

 to a great extent, with ova that had been twenty-four hours in water, the temperature 

 during the period ranging from 18 Cent. (64'4 FAHR.) to 22 Cent. (71'6FAHR.), and 

 with some eggs that had not been immersed even at thirty- six hours;}:, the temperature 

 being then from 12 Cent, to 15 Cent. (53'6 to 59 FAHR.). The results obtained by 

 myself have been much less successful. Out of one hundred and forty ova obtained 

 from a female frog, killed twenty-four hours before and preserved at or below the tem- 

 perature of 55 0< 5 FAHR., at which the experiment was made, only a very few became 

 partially segmented, but not one produced an embryo ; although an abundance of im- 

 pregnating fluid, abounding with spermatozoa, and obtained only a few minutes before 

 it was employed, had been supplied to them. It is evident therefore that this failure 

 was due chiefly to the ova, and not to inefficiency of the impregnating fluid. On the 

 other hand, I have been equally unsuccessful with ova from a frog that had been 

 killed only two hours and a half when the impregnating fluid employed had been 

 more than four hours and a half mixed with water. In this case the failure appeared 

 to have been due chiefly to the spermatozoa, nearly the whole of which, on inspection 

 by the microscope, were found to be motionless and appeared to have lost their vita- 

 lity. At the same time it must be mentioned that the female from which the ova 

 employed in No. 3 of the last set of experiments were obtained still existed, in so far 

 as the vitality of the muscular system was concerned, and therefore can hardly be 

 mentioned in comparison with MM. PREVOST and DUMAS' observation. But while the 

 numerical results obtained by myself have been less favourable than those of SPAL- 

 LANZANI or the physiologists now mentioned, the general facts, so far as they are open 

 to comparison, are in full accordance with them. The difference in the details of 

 our respective observations appears to have been due in chief part to the influence of 

 temperature at the time of the impregnation of the ova, or within the first two or 

 three hours after the impregnating fluid has been supplied. Thus, if the temperature 

 * Dissertations, &c., vol. ii. p. 177. f Loc. cif., vol. ii. p. 140. } Id., p. 134. 



