28O J. T. PATTERSON AND H. L. WIEMAN. 



condition, so characteristic of the sperms in the ordinary eggs, 

 which already possess the completed spindle. It should also 

 be noted that we have occasionally observed non-fertilized 

 uterine eggs which contained the unmodified germinal vesicle. 



What we have just stated is further confirmed by observations 

 on eggs that were fixed soon after they were laid. In certain 

 phases of the contraction stage the spindle fails almost entirely 

 to take up the haematoxylin stain, so that in studying such 

 material one gains the impression that in at least some of the 

 eggs the spindle has retrograded, or has even completely dis- 

 appeared. However, if sections from the same series are stained 

 with safranin and Lichtgriin the spindle stands out clearly and 

 distinctly and is found in practically every egg. 



This, together with the further fact that abnormal spindles 

 are sometimes found, might easily lead the observer to conclude 

 that a degeneration of the uterine spindle takes place. However, 

 a careful study of a complete series of stages will convince anyone 

 that such is not the case. We have been able, by the means of 

 such a series, to follow the entire history of the uterine spindle, 

 from the time of its first appearance up to the formation of the 

 first polar body. The early phases of the spindle have already 

 been sufficiently dealt with, and the rest of the history, from the 

 contraction of the spindle to the formation of the polar bodies, 

 follows. 



The contraction of the spindle is a characteristic phase of the 

 process of maturation, and occurs at about the time of ovi- 

 position or shortly thereafter. The spindle shortens to less 

 than half its original length (cf. Figs. 6 and 10). During the 

 shortening the astral centers of the spindle draw closer together 

 and gradually stain less and less deeply. This is probably what 

 Selenka and others refer to when they speak of the polar suns 

 drawing together and growing faint. The end result of the 

 shortening is the production of a short, relatively thick spindle. 

 The shortening usually begins when the spindle starts to move 

 to the surface, but in some eggs the process is completed while 

 the spindle holds an approximately central position (Fig. 10). 



This process of contraction is by no means unique for Plano- 

 cera, but is characteristic of the first maturation spindle of several 



