G:eRMlNAL VESICLE AND PJItST tlMBRYONIC NUCLEUS. 17^ 



elements, (b) as regards the number of the elements. More- 

 over the interpretation of the observed facts is different. 

 Hertwig regards the refractive corpuscle as a nucleus 

 (Spermakern), and this nucleus is, according to him, only 

 the head of a spermatozoon ; the clear space in which it is 

 seen is occupied by protoplasma belonging to the yolk. In 

 my opinion the clear spot is the nucleus; the transparent 

 corpuscles which afterwards appear are nucleolar elements, 

 the mode of formation of which I have never been able to 

 observe, but which, in my opinion, based upon the time of 

 their appearance, their number, and even their characters 

 cannot be heads of spermatozoa. 



I will make in the first place two observations which are 

 entirely in favour of M. Hertwig. (1.) M. Hertwig has seen 

 the successive phases in the formation of the first cleavage- 

 nucleus produced under his eyes, observing the same egg 

 continue its development on the stage, while my conclu- 

 sions rest on the comparison of a large number of eggs at 

 different stages of development. 



(2.) M. Hertwig's view, with respect to the significance of 

 his spermatic nucleus, rests on a positive fact ; he has seen a 

 line start from this body and become continued beyond the 

 yolk into a spermatic filament. For my own part I have not 

 been able to account for the formation of my nucleolar 

 elements, and my opinion as to their significance rests upon 

 negative facts. 



But all those who have made observations of the kind of 

 which I am now speaking, will acknowledge how easy it is 

 to deceive oneself about the meaning of a delicate line ob- 

 served in the yolk of a large egg. It is easy to deceive one- 

 self with respect to the continuity of such a line with a 

 spermatic filament contained in a narrow space between the 

 yolk and the ovular membrane. Hertwig, on the other hand, 

 says himself that he has never seen a spermatozoon bury its 

 head iu the yolk, and this head become his spermatic nu- 

 cleus. Hertwig's direct proof is then still wanting. 



As to the opinion which Hertwig has expressed with respect 

 to the nuclear nature of his spermatozoon-head, it appears to 

 me that little can be said for it. I see no reason for calling 

 the little body which he regards as the head of a sperma- 

 tozoon, a cell-nucleus. The clear spot in which is contained 

 the homogeneous corpuscle seems to me to present rather the 

 character of a nuclear element. Still the name of celU 

 nucleus cannot be given either to the clear spot or to the 

 corpuscle contained in it ; for the element looking like a 

 nucleus which is formed near the surface of the yolk does 



