CELL INCONSTANCY IN HYDATINA SENTA 457 



dividual was a young one which had not yet undergone all its 

 cell divisions, or that distortions concealed one or more of them. 

 However, he finally concluded from the positions of the remain- 

 ing cells, and from supposed protoplasmic remnants, that cer- 

 tain cells had been lost, and suggested that their disappearance 

 was due to the diatomaceous food upon which the animals were 

 reared. So convinced was he that the number of cells in each 

 and every organ is constant, that in the summary of the paper 

 cited, the possibility of exceptions is practically ignored. 



Such regularity in this rotifer is surprising to one who has 

 noted its extreme irregularity in other respects. The metab- 

 olic processes'^ which result in cell division, and determine the 

 number of cell divisions, must needs occur with clock-like pre- 

 cision; while the metabolic processes that determine the rate of 

 growth and the type of reproduction are subject to great and 

 unaccountable fluctuations. The remarkable contrast of fixity 

 in one set of processes, and apparent lawlessness in another, 

 in the same animal led me to examine a very limited portion of 

 the structure of this rotifer to ascertain whether the number of 

 cells is as nearly constant as Martini supposed. 



For the proposed test, two small organs whose cells could be 

 easily counted were selected. These were the yolk gland and 

 the gastric glands. The yolk gland is a large syncitial mass, 

 in the form of a baseball catcher's mitt, closely applied to the 

 stomach-intestine and to the ovary; it was found by Martini 

 to have invariably eight nuclei. The gastric glands are two 

 rounded masses, situated near the upper end of the stomach- 



' By ascribing the initiation of cell division and the determination of the 

 number of cell divisions to metabolic processes I do not attempt to locate the ul- 

 timate cause. I have on one occasion verbally expressed the view that in some 

 way the number of cells is dependent upon some rhythm of the protoplasm. Here 

 again, 'rhythm' is not supposed to name the final agent. Even if cell constancy 

 were attributed to an accurate time relation between the rhythm of cell division 

 and the rhythm of growth and differentiation, such that a given number of cell 

 divisions (no more and no less) had time to occur before cell differentiation made 

 further division impossible, the assumed rhythms would not be the ultimate 

 cause. Doubtless something inherent (hereditary) in the organism determines 

 these rhythms, as is almost certainly true of the rhythm in the life cycle; but 

 this inherent something must work through metabolic processes to attain its end. 



