278 J. T. PATTERSON AND H. L. WIEMAN. 



so far as we have observed completes the division cycle; at least 

 not while the ovum is still in the uterus. 



We believe that these abnormal spindles are the result of 

 unfavorable conditions arising principally from not removing 

 the worms from the whelk soon enough after the latter are taken 

 from the sea, or perhaps from some other pathogenic cause, for 

 they do not have any part in the normal development of the egg. 

 Whether or not such eggs develop after being laid is a question 

 we have not entered into. It may be that the presence of a few 

 such spindles among normal ones in the uterus has led other 

 observers to believe that they were stages in the supposed dis- 

 integration of the normal uterine spindle. In fact, we were 

 inclined toward such an interpretation until, largely as a result 

 of exercising greater care in handling the living material, we 

 obtained worm after worm in which the uterus does not show a 

 single abnormal mitotic figure. 



III. THE LAID EGG. 



The condition of the laid egg of Planocera has been described 

 both by Wheeler ('94) and by Surface ('07). According to 

 Wheeler, the nucleus returns to a resting condition during or 

 just before the egg is laid, and Surface states that it contains 

 a large germinal vesicle which is situated slightly to one side 

 of the center. We are unable to confirm these observations. 

 In the first place, we find a considerable variation in the con- 

 dition of the freshly laid eggs. Usually such eggs show that the 

 so-called uterine spindle has undergone, or is in the process 

 of undergoing, contraction, just prior to its migration to the 

 surface to give rise to the first polar body. 



The varying conditions of which we have just spoken consist 

 almost altogether in the state of contraction or shortening 

 shown by the spindle at the time the egg is laid. The most 

 extreme cases are those in which the shortening is completed and 

 the spindle has already migrated to the surface of the egg. 

 Indeed, we have one lot of eggs (laid July 25, 1912) which were 

 killed immediately after they were laid, and in which one occa- 

 sionally finds eggs having the first polar body well started or com- 

 pletely formed. These variations in the condition of the spindle 



