456 A. FRANKLIN SHULL 



How rigidly the factors producing cell constancy must oper- 

 ate, therefore, is a matter of some importance. If the number of 

 cells is absolutely invariable in the adult, as well as in the em- 

 bryo, the explanation of constancy must be of one kind; if the 

 adult number is occasionally aberrant, while the embryonic 

 number is invariable, the explanation may be of a somewhat 

 different order of exactitude. Regarding the invariability of 

 the adult number one is left somewhat in doubt by the state- 

 ments of Van Cleave and of Martini, chiefly because it is not 

 usually stated just how many individuals have been studied. 

 Van Cleave (op. cit., p. 259) states that, in his work, in no case 

 was the number of individuals examined as small as two, and 

 that in many cases it was as large as two hundred. He reports 

 no variations in the number of cells in any organ, except possibly 

 one in which the number of cells was so large that it was difficult 

 to count them accurately. The one possible exception was pre- 

 sented by two individuals, studied by the reconstruction method 

 from sections, which revealed, respectively, one hundred and 

 eight and one hundred and nine cells in the brain, with the pos- 

 sibility that one of these counts was an error. Van Cleave him- 

 self raises the question whether moderate variability would in- 

 validate conclusions drawn from cell constancy, but since he 

 concludes that no such moderate variability was demonstrated, 

 nor even rendered probable, in Eorhynchus, the question was not 

 very pertinent to his own work. 



Martini ('12) expresses the conviction that the number of 

 cells in the rotifer Hydatina senta is highly invariable. He 

 states the number of cells (or nuclei, in the case of syncitia) in 

 each organ, adds them together, and gives the total number of 

 cells for the whole organism as nine hundred and fifty-nine. 

 In most of the organs, especially the smaller ones, the number of 

 cells was never found to vary. In others there was some un- 

 certainty. The stomach-intestine, for example, usually con- 

 tains thirty cells, but in a few instances an aberrant nmnber was 

 found. Martini strongly emphasizes that the aberrant number 

 were always less than thirty, and he was at first inclined to as- 

 cribe the reduced number to the probability either that the in- 



