1 88 J. THOMAS PATTERSON. 



bodies. The first maturation follows immediately upon the 

 fusing of the chromosome vesicles produced by the aborting 

 spindle, and at the time it occurs the sperm is already present 

 in the egg (Fig. 21). The demonstration of maturation as taking 

 place simultaneously in the two eggs within the same capsule 

 is the most cogent proof we can offer against the idea that this 

 animal exhibits polyembryony; because if this is a fact, each egg 

 must subsequently be fertilized before it could develop, and that 

 would at once remove the case from the category of polyembry- 

 ony; and even though no other proof could be offered, such as 

 we have given in connection with the section on the formation 

 of the capsule, this would be sufficient to establish our main 

 contention. As a matter of fact we have found two very clear 

 cases in which each of the two eggs is undergoing maturescence. 



The egg in one of these shows the first maturation spindle in 

 the anaphase (Fig. 20). The spindle is extremely large and has 

 at each end a large aster with very conspicuous centrospheres, 

 in the lower of which is a single centrosome and in the upper of 

 which are tw r o centrosomes. The sperm head, already showing 

 signs of its transformation into a pronucleus, lies near the lower 

 aster. Between the upper pole of the spindle and the egg- 

 membrane is a clear space due to a depression in the egg at this 

 point. In a slightly later stage the egg elongates in the direction 

 of the long axis of the spindle, taking on an appearance much 

 like that of a pear, with the smaller end representing the animal 

 pole. A very large polar body is then cut off, and the mate to 

 this egg fortunately shows this process going on (Fig. 24). Since 

 the first cleavage division results in producing a micromere of 

 about the same size, opportunity is afforded for confusing this 

 cell with tin- first polar body, but. the difference can easily be 

 told if the chromosomes arc in a condition that allows their 

 enumeration to be- made. 



In the second case one of the eggs (Fig. 22, on the left) sho\\> 

 the maturation spindle in prophase with four distinct tetrad^, 

 and the other cell a polar view, in which only three chromosomes 

 appear. I have been unable to find a totinh tetrad, and I theiv- 

 fore assume that it must have been destroyed by the knite. 



Several eggs showing the first polar body just extruded have 



