208 MR. NEWPORT ON THE IMPREGNATION OF 



some of these the body appeared to be slightly enlarged. Segmentation commenced 

 in very many of these ova in five hours and ten minutes, and was almost universal in 

 them a few minutes later. Nearly the whole of these ova produced embryos, there 

 being only nine out of the one hundred and thirty that were abortive. I have some- 

 times found a much larger proportional number of unproductive ova in some broods 

 in the natural haunts of the Frog. 



There was one exceedingly interesting fact in this experiment, it was that the 

 smaller and apparently less matured ova were as fully impregnated as the larger and 

 more perfect. The whole set of observations was the more interesting from this cir- 

 cumstance. These ova were smaller than usual and had not the white surface so com- 

 plete, but were very like the ova in which I have described the changes in the light- 

 coloured surface (p. 185). When first placed in water with the filter paper and 

 spermatozoa, the surface of the yelks became more contracted and irregular, within 

 the vitelline membrane, than in other ova I have employed. Hence I had much 

 doubt, at first, whether any satisfactory evidence would be obtained from this set. 

 But the contrary has been the case, as it is evident that some ova may be impreg- 

 nated at a little earlier period than usual ; and that when a great abundance of sper- 

 matozoa is supplied, ova less matured than others may be equally well impregnated. 

 The greater efficiency of a larger as compared with a smaller number of spermatozoa, 

 with reference to the earlier or later segmentation of the yelk, has already been 

 shown ; and the difference is very marked in the first and third of this set of experi- 

 ments, both with reference to the occurrence of segmentation and to the relative 

 fecundity of the ova. On the other hand, the experiment No. 2 proved that the 

 liquor seminis is not the fecundating portion of the seminal fluid. 



Circumstances having prevented me from making known the result of these expe- 

 riments at the time they were obtained, I determined, during the past spring, to 

 repeat and vary them, to obtain, if possible, still more conclusive proofs that the 

 spermatozoa alone effect impregnation. Accordingly, in March and April of the pre- 

 sent year (1850) I repeated them, with the following precautions : first, that the frogs 

 in each case had been some days paired, and at the time of the experiment were 

 nearly ready to spawn ; next, that the seminal fluid used was obtained from the male 

 paired with the female from which the eggs were taken ; further, that the condition 

 of the specimen of fluid used was correctly ascertained ; and lastly, that the ova 

 were placed in flat dishes, under precisely similar circumstances, with similar quan- 

 tities of water, repeatedly changed. Two sets of experiments were made at the same 

 time. 



Set M. April 4, 1850. Atmosphere 60 FAHR. 



The seminal fluid employed, mixed with an equal quantity of water, was placed on a 

 single, and caught on a double filter paper, and the clear fluid that passed was then ex- 

 amined with the microscope. The fluid that had traversed the three filters was almost 

 completely deprived of spermatozoa ; as, after many very careful examinations, both 



