MALE AND FEMALE PEONUOLBI. 33- 



reticulum to a state in which it is condensed into the chro- 

 matin masses of forms a, c, and d. 



In the subsequent stages of segmentation the nucleus 

 gradually becomes smaller until at the close of segmentation it 

 has an oval form with a long diameter of 0'016 mm. It now 

 presents the features described by Flemming and other obser- 

 vers in the nuclei of the salamander and other animals. 



During segmentation the nucleus generally has the third 

 form above described : I have never seen it in a spherical, and 

 only once in a spindle form. I conclude that these forms, if 

 they occur^ are very rapidly passed through. 



2. The Female and Male Pronuclei. — I include under this 

 head the nucleus of the ovum after the formation of the first 

 polar body. I have no observation on the nucleus of the 

 uterine ovum before this event. 



a. Two Ova of Peripatus Balfouri with one polar 

 body completely formed and no trace of the second. — 

 In one the nucleus of the ovum had the spindle form and the 

 two equatorial rows of chromatin bodies had already slightly 

 separated from one another. It was placed near and with its 

 long axis parallel to the surface of the ovum. The area of 

 dense protoplasm in which it was placed was considerably 

 smaller than in later ova which possessed the first segmenta- 

 tion nucleus. The spindle had a length from pole to pole of 

 •017 mm. It presented precisely the same features of structure 

 as the larger spindle described above. 



In the other ovum the nucleus had the form of a number of 

 closely aggregated masses of chromatin occupying an area of 

 •0084 mm. The protoplasm in which these masses were con- 

 tained did not appear to differ in any way from the rest of the 

 denser protoplasm of the animal pole. 



Male Pronucleus. — On the side of the ovum opposite to 

 the nucleus, and nearly in the same transverse plane, was a 

 small lobed mass of chromatin having a diameter of ^0042 mm. 

 It was contained in a very small area of protoplasm in which 

 the network was dense as at the opposite pole. This I take to 

 be the male pronucleus, 



