20 C. ISHIKAWA. 



matic elements belonging to both the nuclei nre still to l^e seen in two 

 separ.'ite gr(^nps. In these tln*ee sections as well as in those i-epresented 

 bv the next tliree tignres the nnnilier of the chromatic elements is not 

 at all clear. Fig. .52 shows a cross section of a spindle at the stage 

 sliown by fig. 51, more highly magnified. Figs. 53 and 54 are 

 taken from the same lot of eggs as tliat represented by figs. 51 and 52, 

 bnt the chromatic elements are fused together at flie equator of tlie 

 spindle, and are now no more to be distinguished as two separate 

 groups. 



Lastly in fig. 55 is found tlie first segmentation-spindle with 

 the chromosomes just separating from the ecinatorial ])laiie. Tlieir 

 nu.mber can be distinctly counted as eight in t\V(i rows, one of wliicli 

 at tlie riglit hand side happened to be pulled Iw the acliromatic filires 

 of tlie left, and is seen witli its one end at the riglit and the other at 

 tlie left. 



P.. SUMMARY. 



1. The primary sperm cells correspond exactly \Yith the primary 

 eg^'-cells. lîoth contain eight chromatic elements. 



2. In fx^th cells the eight chr<^mosomes become constricted 

 transversely giving rise to eight dumb-bell shaped bodies. Tliese 

 arrange themselves m an equatorial zone and begin to di\ide in such a 

 manner that half of each clu'omosome goes to one cell and the other 

 half to the otlier. Tins kind of cell-division takes place two or 

 three times and the resulting cells fn-m the mother cells of eggs or 

 sperniatt)Zoa, as the case may be, 



3. These grow consideralily ; after which 



4. They begin to di\ide as ])efore ; each chromosome dividing 



