464 A. FRANKLIN SHULL 



eighteen. More likely the number would be between these, 

 since there is nothing as yet to indicate that deviation in one 

 organ is associated with deviation in other organs. However, 

 the possibilities are numerous, not single. If each organ contains 

 unusual numbers of cells in 5 per cent of the individuals, and 

 there is no association between the deviation in various organs, 

 the total number of nine hundred and fifty-nine would probably 

 be realized less often than not. 



It has not seemed worth while to pursue the re-examination of 

 cell constancy in Hydatina further than the two organs named. 

 A measure of its exactitude has been obtained, and that is all 

 that was sought. The observations described in this paper do 

 not destroy the problem of cell constancy; they merely make its 

 solution easier. Even if every organ of every animal in which 

 constancy of cell numbers has been claimed, should prove to be 

 as variable as the yolk gland and gastric gland of this rotifer, 

 the problem of cell constancy would remain. Although the total 

 number of cells in an organism is the same in only a small per- 

 centage of cases, if the number in any one organ is the same in 

 ninety per cent of the individuals, there is a problem of cell 

 constancy which calls for solution. But there is no need of com- 

 plicating this solution by assuming a degree of constancy that 

 does not exist. 



BIBLIOGRAPHY 



Martini, E. 1909 a Studien iiber die Konstanz histologischer Elemente. I. 



Oikopleura longicauda. Zeit. f. wiss. Zool., Bd., 92. 



1909 b Studien, u.s.w. II. Fritillaria pellucida. Zeit. f. wiss. 



Zool., Bd. 94. 



1909 c iJber Subcuticula und Seitenfelder einiger Nematoden. IV. 



Vergleichend-histologischer Teil, Zeit. f. wiss. Zool., Bd. 93. 



1912 Studien, u.s.w. III. Hydatina senta. Zeit. f. wiss. Zool., 



Bd. 102. 

 Van Cleave, H. J. 1914 Studies on cell constancy in the genus Eorhynchus. 



Jour. Morph., vol. 25. 



