172 MR. NEWPORT ON THE IMPREGNATION OF 



of the semen appears to be constituted almost or entirely of spermatozoa, while 

 scarcely any liquor seminis can be detected ; and further, on the great improbability, 

 perhaps impossibility, of the liquor seminis of those animals which expel their ova 

 into water before impregnation being brought into contact with the ovum. But the 

 same author justly remarks, that " even up to the present day this hypothesis of the 

 influence of the liquor seminis has not met with any direct refutation." To this I 

 may add, that however strong the presumption may be in favour of the agency of 

 the spermatozoa in those instances in which a liquor seminis has not been observed, 

 it affords no sufficient reason for disbelieving that the spermatozoa are not resolved 

 into fluid at the moment of fecundation ; or that in those animals in which the liquor 

 seminis occurs in abundance it is not that which impregnates the ovum. 



The question then, so far as proof is concerned, both of the direct agency of the 

 spermatozoa, and of the non-efficiency of the liquor seminis in impregnation, remains 

 open, as well also as that which involves the knowledge as to how impregnation is 

 effected. 



It is to these questions that this communication which I have now the honour of 

 laying before the Royal Society is chiefly directed. I propose^r*# to show the time 

 and mode of disappearance of the germinal vesicle, and the condition of the ovum in 

 the Frog and Newt, immediately before and after impregnation, and to endeavour to 

 supply proof from actual experiments that the spermatozoa alone, in all cases of com- 

 munion of the sexes, are the sole agents in impregnating the ovum ; and further, that 

 impregnation cannot be effected by the liquor seminis ; and next to examine in what 

 way the agency of the spermatozoa is influenced, impeded, or exerted. 



1. CHANGES IN THE OVUM WITHIN THE BODY. 



The ovum of the Amphibia has so frequently been the subject of examination by 

 the best observers that a further detailed account of its development may at first ap- 

 pear to be useless, after what we already know of its changes through the labours of 



SWAMMERDAM, LEEWENHOEK, RoESEL, SPALLANZANI, PflEVOST and DuMAS, RuSCONI, 



BAER, REICHERT, VOGT, BELL and others. But apart from the fact already men- 

 tioned, that the ovum of the Amphibia affords us the best means of actual experiment 

 on impregnation, there are questions which relate to its earlier conditions on which 

 the observers named are not agreed, but which are of importance with regard to the 

 physiology of reproduction in the whole of the vertebrata. 



I shall state, therefore, what I have myself observed with regard to these questions 

 from the time when the ovarian ovum is approaching to maturity to that of its expul- 

 sion from the body, before entering on the subject of its impregnation. 



As our means of comparing and testing the accuracy of all observations in natural 

 history, and of experimental results in physiology, depend mainly on the correct 

 identification of the objects examined, I may here state at once that the objects of 

 the following details have been the Frog, Rana temporaria, and the Toad, Bufo vul- 



