CELL CONSTANCY IN THE GENUS EORHYNCHUS 255 



ular procedure of cleavage and development up to this point has 

 been very generally demonstrated in the forms whose cell lineage , 

 has been determined, but it was left for such men as Weismann, 

 Goldschmidt, and Martini to raise the question of a probable 

 further continuation of an orderly process. It was already known 

 that in many instances certain cells are very early set apart for 

 the formation of definite groups of organs or tissues, but no one 

 had actually determined how these organs arise, whether by mere 

 indeterminate continuation of the process of cell division, or in an 

 orderly, specifically predetermined manner. Might not the same 

 forces at work upon and within the embryo during its cleavage 

 stages continue to direct an accurately determined continuation of 

 the cleavage throughout the course of development until the adult 

 form is gained? The works of Goldschmidt and of Martini go 

 a great way toward the confirmation of this hypothesis, at least 

 within certain groups of animals. Their results indicate that in 

 the forms studied mitosis has continued along very definite lines, 

 resulting in a predetermined arrangement of the cellular elements 

 of the adult organs and tissues. In his definition of cell constanc y 

 Martini institutes a comparison, not alone of the numbers of n u- 

 clei and their relative positions, but also of the size, shape, and 

 finer structure of the cells, and especially of the staining reactions 

 of the nuclei of the cells. 



The writer is surprised to find no reference in the more recent 

 literature on cell constancy to Weismann' s exceptionally clear 

 ideas as regards the phenomena of constancy. He writes on this 

 point('93, p. 59): 



In smaller and simpler organisms each individual cell may well be 

 determined from the germ onward, and not only with the result that the 

 number of cells is a definite one,' and the position of each definitely local- 

 ized: the determination may also have caused individual peculiarities 

 of each cell, in so far as they depend on changes in the germ plasm at 

 all — i.e., are 'blastogenic,' — to appear in the corresponding cell in the 

 next generation. 



Such a statement of the fundamental principles underlying the 

 theory of cell constancy coming from such a clear thinker as 

 Weismann, even though at the time unsupported by any mass of 



