NUCLEAR CONSTANCY IN HYDATIXA. 89 



clency for the nuclei to occur in definite arrangement. Before 

 the gland has reached its full functional stage in development 

 the nuclei (Fig. 2) frequently assume the same definite orderli- 

 ness of arrangement characteristic of the mature female (Fig. i). 

 Typically, the 8 nuclei are arranged in the form of a letter V ex- 

 tending across the body with the base of the V at the lateral mar- 

 gin that is contiguous to the ovary. In such instances there is an 

 anterior row of 4 nuclei, a posterior row of 3, and a single nucleus 

 lying near the margin midway between the two rows. This usual 

 arrangement of the nuclei is described because it seems to throw 

 some light upon the question of the interpretation of the aberrant 

 individuals that have been observed in the course of this study. 



With but three individuals displaying aberrant numbers of 

 nuclei in the vitellaria the writer realizes that the material is too 

 meagre to permit of broad generalizations. Since, however, all 

 three of these specimens have so many characteristics in com- 

 mon, it seems that the line along which the abnormal condition has 

 been reached must have been fairly uniform. In the two indi- 

 viduals having 10 nuclei in each vitellarium (Figs. 7 and 8), there 

 is strong evidence that the two accessory nuclei have resulted 

 from a division of two nuclei in the region of the ovary. Thus 

 each transverse row contains an additional nucleus. Arrange- 

 ment of the nuclei in the vitellarium having 12 nuclei (Fig. 9) 

 very strongly supports the hypothesis that this condition has 

 arisen from the typical vitellarium with 8 nuclei through a supple- 

 mentary division of two nuclei of each transverse row thereby 

 adding 4 nuclei to the normal number. The time at which this 

 division occurred cannot be determined from an examination of 

 the specimens. In any of the three instances mentioned above 

 the non-conformity of nuclear numbers may have been brought 

 about either by the failure of certain nuclei to lose their power of 

 mitotic division at the accustomed stage in the development of the 

 organ or through some sort of stimulation of certain nuclei of a 

 normal mature organ to undergo either mitotic or amitotic divi- 

 sion. Evidence observed in the course of this study seems to 

 point toward a late amitotic division occurring in the mature 



organ. 



