AND ON THE DIRECT AGENCY OF THE SPERMATOZOON. 247 



absent from any egg which has produced an embryo. Its formation is preliminary to 

 the subsequent cleavage of the yelk. It thus affords, within a very, short space of 

 time, a certain test of fecundation, and as such is exceedingly valuable in all experi- 

 ments by artificial impregnation. 



7. PARTIAL, OR INCOMPLETE FECUNDATION. 



But although the formation of the chamber gives certain proof that the egg has 

 been influenced by the spermatozoon, it is only the actual segmentation of the yelk, 

 carried through the first four stages, which shows that its fecundation has been com- 

 pleted ; since the egg may be only partially influenced, and consequently may not 

 produce an embryo, although the respiratory chamber may be formed, and the early 

 stages of segmentation of the yelk be commenced. When this is the case the change 

 seldom proceeds beyond the second or third stage of cleavage, and even then there is 

 usually some irregularity in its occurrence. Sometimes only the chamber itself is 

 developed, and the process then stops ; at other times the chamber is completed and 

 a little white spherical body makes its appearance, and is but just perceptible within 

 the entrance to the central canal ; but more frequently a white spherical body, not 

 more than one-fourth the size of the original germinal vesicle, appears on the surface 

 of the yelk within the chamber ; at other times there are two of these white bodies, 

 each of which is scarcely more than one-half the size of the single one, and sometimes 

 the bodies are of a dark or grey colour. In other cases the yelk begins to be divided 

 in the margins of the canal, but does not proceed with its change ; or it may go on, 

 as just stated, to the several stages. In other cases the yelk divides very unequally. 

 These instances of partial impregnation or fecundation may occasionally be produced 

 by application of exceedingly minute quantities of seminal influence, as some of the 

 following experiments will show. 



8. DEFICIENCY OF FECUNDATORY INFLUENCE. 



(a.) Pin-point application of the fluid. These experiments were commenced in the 

 season of last year (1851), but have been repeated at different periods during the 

 season of the present year. 



March 30, 1851. Atmosphere 56FAHR. A single egg was passed into each of 

 four glass cells, with a small quantity of water, sufficient only to preserve the eggs 

 moist and promote the expansion of their envelopes. Within two minutes afterwards 

 two of the eggs were each touched once with the point of a common-sized pin, which 

 had been so lightly dipped, into a mixture of one part of fecundatory fluid, obtained 

 about one hour and five minutes before, and four parts of water, as to cover a por- 

 tion of its surface equal to about one thirtieth of an inch in extent. The two remain- 

 ing eggs were touched, the first once only, and the second twice, with the point of a 

 pin slightly curved, and which thus was made to retain a much greater number of 

 spermatozoa in the fluid which adhered to it than the pin with the straight point. 



