284 H. J. VAN CLEAVE 



the body is evidenced by the results obtained by Morgan in 

 his experiments upon the embryos developed from isolated 

 blastomeres of echinoderms and of chordates. In 1896 he found 

 that the larvae of Amphioxus developed from isolated blastomeres 

 of the two and four cell stages tend to utilize the same number 

 of cells for the formation of the organs of the body as do the normal 

 larvae. In the formation of the gastrula stage the normal larvae 

 invaginate about one-tenth of the total number of cells present 

 in the blastula. Thus in a one-half or a one-quarter embryo, 

 while the number of cells in the blastula is not as great as the num- 

 ber in the normal blastula, the actual number of cells that is in- 

 vaginated tends to equal the number invaginated in the whole 

 embryo. In other words, it seems as though a definite number 

 of cells were necessary for the formation of a given organ of the 

 body. ''I have been personally most loath," he adds, 'Ho accept 

 this conclusion, because it seemed a priori very improbable that 

 a numerical question could enter into this problem, but I see no 

 other alternative than to accept this view of the matter." It 

 would seem that if this be the case in organ formation, the re- 

 quirement is one rather of the number of cells entering into th5 

 composition of the organ, than a mere quantative regulation or 

 partition of the amount of protoplasm. 



The controversy over the relation between the cell size and body 

 size may be taken too seriously. The writer has pointed out the 

 various possible relations between body size and cell size. The 

 problem does not involve a fundamental conception under which 

 all data must be subsumed and made to agree. Different groups 

 of animals may vary widely in respect to the possibility of a 

 direct correlation between the two, the only problem of real con- 

 cern is to what extent any given condition is fixed within a given 

 group of organisms. In fact Morguhs ('11) has shown experimen- 

 tally that the relation of cell size to body size may be altered in 

 the individual through a change of physiological conditions. In 

 connection with his observations on complete inanition he has said 

 ('11, p. 259) : "In the case of Diemyctylus it was found that the 

 volume of both the cells and nuclei of different tissues diminishes 



