NUCLEAR CONSTANCY IN HYDATINA. 93 



this solution by assuming a degree of constancy that does not 

 exist." In speaking of the results of his own work on cell-con- 

 stancy in Hydatina he has maintained that he has obtained " A 

 measure of its exactitude" as expressed in his finding 4 per cent, 

 of individuals bearing inconstant numbers of nuclei in the vitel- 

 larium and 7.5 per cent, showing aberrant numbers of nuclei in 

 the gastric glands. 



In contrast with these observations stand those included in the 

 present paper wherein a much greater number of s individuals 

 were examined, and yielded less than 0.4 per cent, inconstant vi- 

 tellaria and absolute constancy in the gastric glands. 



The complete absence of subnormal numbers of nuclei from the 

 data presented by the present writer seems especially significant in 

 that it indicates that the mechanism operating to bring about con- 

 stancy of nuclear numbers has operated to its full extent and that 

 any abnormalities represent an inconstancy secondarily imposed. 

 Reductions in nuclear numbers might also result from secondary 

 causes but the writer has seen no evidence of factors operating 

 in the regions studied to bring about a reduction in the numbers 

 of nuclei. 



As a result of his observations, Shull seems to have full con- 

 viction that the tendency to vary is inherent in the nuclear num- 

 bers of Hydatina regardless of circumstances such as culture 

 medium and strain. If his conclusions in this regard are valid, 

 either some factor or group of factors not considered by Shull 

 have been operating to suppress the inherent tendency to vary in 

 the particular culture studied by the writer or physical difficulties 

 involved in reconstructing and counting the nuclei from serial 

 sections have introduced an element of error into his results. 



LITERATURE CITED. 

 Martini, E. 



'12 Studien iiber die Konstanz histologischer Elemente. III. Hydatina 



senta. Zeitschr. f. wissensch. Zool., 102: 425-645. 

 Shull, A. F. 



'18 Cell Inconstancy in Hydntina senta. Jour. Morph., 30: 455-464. 

 Van Cleave, H. J. 



'14 Studies on Cell Constancy in the Genus Eorhynchus. Jour. Morph., 25 : 



253-298. 



'20 Two New Genera and Species of Acanthocephalous Worms from 

 Venezuelan Fishes. Proc. U. S. Natl. Mus., 58: 455-466. 



