88 John H. Gerould, 



of Brussels that he has found the same number in the egg of 

 Sipimcidiis nudns. A chromosome in the earliest condition which I 

 have observed is shaped like an elongated link in a chain (Fig-. 3, 

 4), or like a rod fashioned into an ellipse. Tliis ellipse breaks apart 

 in the middle, either completelj^ to form two U-shaped fig-ures with 

 the curves extending- toward the poles of the spindle, or partially, 

 i. e. on one side only. In the latter way the ellipses become trans- 

 formed, as I believe, into the longer straig^ht rods, which terminate 

 in knobs that are bent to one side (Fig. 4). These rod-shaped 

 chromosomes, w'hich are sometimes further modified by other varico- 

 sities than those at their extremities, eventually break in two in 

 the middle and diverge towards the respective poles of the spindle 

 (Fig. 7). Thus the formation of the first polar body probably in- 

 volves a transverse division of the chromosomes of the oocyte, or a 

 „reducing division" in Weismann's sense. I have not succeded in 

 following the changes in the chromosomes in the stages preliminary 

 to the metaphase of the first polar spindle; but, at this time, the 

 chromosomes are always, in hundreds of eggs that I have observed, 

 arranged parallel to the length of the spindle. In no case have I 

 seen cross-shaped chromosomes in PhascoJosoma, such as Griffin 

 described in Thalassema, which aiforded him evidence of the gradual 

 longitudinal division of the chromosomes. On the other hand my 

 observations agree with those of Henking (1891) on Pyrrhocoris and 

 of Paulmier (1899) upon Anasa. PhascoJosoma thus affords another 

 example of "Praereductionstheilung" of Korschelt. 



Third Period: Formation of the Second Polar Body 

 and the Enlargement of the Sperm Nucleus and of its 

 Astrosphere (25—35 minutes after the approach of the spermato- 

 zoon). While the egg nucleus passes from the telophase of the first 

 polar spindle into the prophase of the second (Fig. 9, 10, 16), the 

 sperm nucleus begins to increase in size. The compact mass of 

 chromatin in the sperm head becomes separated into a loose network, 

 as absorption of cell sap into the pronucleus goes on. By the time 

 that the second polar body has been formed, the sperm nucleus has 

 attained its maximum size, and its astrosphere, situated near the 

 middle of the egg, has become enormously enlarged, so that its 

 diameter sometimes exceeds that of the sperm nucleus itself (Fig. 16, 

 17, 18). It usually consists of two concentric vesicles, A minute 

 deeply-staining centrosome is suspended in the centre of the inner 

 vesicle, and from it linin fibres radiate outward to the periphery 



