TF. G. Van Name — Embryology of EustylocJms. 271 



same. Near the periphery of the germinal vesicle a part of the 

 nuclear network can be seen to increase in thickness and stain more 

 deeply. It continues to thicken and assumes a beaded outline, 

 showing that it is composed of minute masses or grains of 

 chromatin, connected together (Fig. 2). Whether this is already 

 broken up into segments representing the future chromosomes, when 

 it first becomes noticeably different from the rest of the threads of 

 the network, I have not been able to discover, as it is almost certain 

 to be cut at different points by the planes of the section. In the 

 egg shown in Fig. 2 it is pretty evident that it has already broken 

 up into segments. These show no signs of longitudinal cleavage in 

 anticipation of the division of the chromatin between the egg and 

 the first polar body. They contract into rounded or oval masses 

 (Figs. 3« and 3^) the chromosomes of the first polar spindle, while 

 the remainder of the nuclear network gradually disappears. 



By this time the asters of the future spindle have become dis- 

 tinguishable (Figs. 2, 3a and 3S). Specimens stained by the iron- 

 hsematoxylin method show that each contains a black staining 

 centrosome (Figs. 3a and 35). 



The question of the origin of these centrosomes is one upon which 

 there is great difference of opinion. Klinckowstrom found the two 

 asters originating separately and simultaneously, their centrosomes 

 lying about -040™™ apart. Van der Stricht's own observations con- 

 firm this; nevertheless he expresses his belief in the claim of 

 Francotte that he has found the centrosome single — "nous le voyons 

 s'allonger, puis se fendiller et se diviser ainsi en deux nouveaux cor- 

 puscules polaires" (3, p. 12). 



In regard to the place and source from which the centrosome or 

 centrosomes take their origin there is also difference of opinion. 

 Klinckowstrom considered them of nuclear origin, basing this belief, 

 however, on a single instance, of which he gives a figure. Van der 

 Stricht believes that they originate from the nuclear membrane 

 and are therefore of nuclear origin. He finds that they afterwards 

 separate from the membrane. Francotte finds the centrosome 

 appearing close to the nuclear membrane, sometimes " si voisin qu'il 

 semble faire corps avec cette membrane," but does not believe in 

 its nuclear origin. 



I have not demonstrated anj^ connection between the centrosomes 

 and the nuclear membrane nor found evidence of their origin by the 

 division of a single body, though this of course may occur before 

 the formation of the aster rays enables us to distinguish tbem. By 



