author's abstract of this paper issued 

 by the bibliographic service, january 12 



CELL INCONSTANCY IN HYDATINA SENTA^ 



A. FRANKLIN SHULL 



Department of Zoology, University of Michigan 



The highly determinate development of certain invertebrates 

 has long been known. The number as well as the fate of the 

 early embryonic cells has been established in numerous cases, 

 and is exceedingly regular. The number of cells in the embryo 

 may be the same in all individuals, even though the number in 

 the adults of the same species is variable. It is only in com- 

 paratively recent years, however, that this constancy of number 

 of cells has been discovered in adult animals of certain species 

 in which the cells are numerous. Martini ('09 a, '09 b, '09 c, 

 '12) has claimed such constancy in nematodes, rotifers, and tuni- 

 cates and Van Cleave ('14) in Eorhynchus. The latter author 

 cites a number of other cases. 



The extension of constancy of cell number to adult animals 

 seems to me to make new demands upon the explanations offered 

 to account for this constancy. Embryonic stages are passed 

 through quickly, and one might suppose that whatever agencies 

 could interfere with the orderly and definite production of cells 

 in the embryo would have little time to do so. Before the adult 

 condition is reached, however, such disturbing factors might 

 have time to operate and the number of cells be thereby altered. 

 The fact of cell constancy in the adult, then, makes greater de- 

 mand upon its explanation than does the fact of cell const ncy 

 in the embryo. I do not mean to assert that the cause of con- 

 stancy in the adult is different from the causes of constancy in 

 the cleavage stages; but an explanation which would satisfy the 

 demands of the latter, might be inadequate for the former. 



1 One entire series of observations on which this paper is based was made 

 possible by part of a grant from the Bache Fund, which I take pleasure in 

 acknowledging. 



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