A DETERMINATION OF THE DEGREE OF CON- 



STANCY IN THE NUCLEI OF CERTAIN 



ORGANS IN HYDATINA SENTA. 1 



H. J. VAN CLEAVE. 



CONTENTS. 



Introduction ........................................................ 85 



Materials .......................................................... 86 



Variability in the nuclei of the vitellarium ............................ 88 



Nuclei of the gastric glands .......................................... cj2 



Conclusions ................. . ...................................... 92 



Literature cited ...................................................... 93 



Explanation of figures ............................................... 9 



INTRODUCTION. 



As a result of his extensive studies on the cytology of Hyda- 

 tina senta, Eric Martini (1912: 631) maintained that each indi- 

 vidual of this rotifer bears a constant total number of 959 nuclei 

 distributed in fixed numbers through the various organs of the 

 body. In other publications, Martini has mentioned the fact that 

 data concerning variability encountered in his studies of cell-con- 

 stancy have been too meagre to permit of quantitative study. His 

 published results on cell-constancy in Hydatina contain no refer- 

 ence to the numbers of individuals examined in reaching his con- 

 clusions of definiteness in cell or nuclear numbers. A. F. Shull 

 (1918), in an attempt to determine the validity of Martini's claim 

 of constancy in histological elements, has made a statistical study 

 of the nuclei in the vitellaria and gastric glands of Hydatina. 

 Contrary to the findings of Martini, Shull has recorded a relative 

 " inconstancy " in the numbers of the nuclei in the organs which 

 he investigated. Thus, Shull failed to find eight nuclei an im- 

 mutable condition for the vitellarium, for in 4 per cent, of his 

 245 specimens observed an aberrant number was recorded. 



Immediately following the appearance of Martini's monograph 

 the present writer became interested in checking over certain 

 minor details of his findings from materials which had been pre- 



i Contributions from the Zoological Laboratory of the University of Illi- 

 nois, No. 192. 



8s 



