94 LECTURES 



tion of impregnation, for example, is concerned even the 

 lucid description given us of it in the common fowl by 

 the late distinguished British embryologist, Mr. Balfour, 

 may not satisfy the minds of all of us as to exactly how 

 life actually begins. Mr. Balfour says that impregnation, 

 in the case of the chicken, "occurs in the upper portion 

 of the oviduct; the spermatozoa being found actively 

 moving in the fluid which is there contained." * * * 



"We have as yet, as far as the fowl is concerned, no 

 direct observations concerning the changes preceding and 

 following upon impregnation; nor, indeed, concerning the 

 actual nature of the act of impregnation." * 



"In other types, however, these processes have been 

 followed with considerable care, and the result has been 

 to show that prior to impregnation a division of the 

 ovum takes place into two very unequal parts. The 

 smaller of these parts is known as the polar body, and 

 plays no further part in the development. In the course 

 of the division of the ovum into these two parts the ger- 

 minal vesicle also divides, and one part of it enters the 

 polar body while a portion remains in the larger segment, 

 which continues to be called the ovum, and is there 

 known as the female pronucleus. Impregnation has been 

 found to consist essentially in the entrance of a single 

 spermatozoon into the ovum, followed by the fusion of 

 the two. The spermatozoon itself is to be regarded as a 

 cell, the head of which corresponds to the nucleus. 

 When the spermatozoon enters the ovum the substance 

 forming its tail becomes mingled with the protoplasm of 

 the latter, but the head enlarges and constitutes a dis- 

 tinct body called the male pronucleus, which travels 

 toward and finally fuses with the female pronucleus to 

 constitute the nucleus of the impregnated ovum." 



From this point it has not proved especially difficult 

 for the trained embryologist to trace the development of 

 the chick of the fowl to that stage of development when 

 it quits the eggshell that incases it during the early 

 stages of its existence. And it may be said that the 

 statements we have quoted from Mr. Balfour may carry 

 with them considerable comfort to him who entertains 

 the biogenetic view of the origination of living matter, 

 still it seems to us that even a little more light in this 

 direction would not come altogether amiss. One, for in- 

 stance, almost fesls Inclined to ask, what is the nature of 

 the life as exhibited on the part of the spermatozoon? I 

 have examined the live spermatozoon of the highest types 

 of vertebrates known to us, and am familiar with the 



