TENOPYR: CONSTANCY OF CELL SHAPE 53 
of stems and roots of many species of plants, reached the same 
conclusion, regarding the size of these cells in large and small indi- 
viduals of the same species, although varieties of the same species 
- may differ greatly as to their cell size. 
Conklin (1912) has made an elaborate and extended study of 
cell size compared with body size in the genus Crepidula. He 
found great variability in the body size of these gasteropods. In 
Crepidula plana, there are dwarf and normal females. These 
latter are larger than the normal-sized males. The average size 
of individuals of the same sex differs greatly for the different 
species. Yet, in spite of all these differences in body size, the tissue 
cells of corresponding organs or parts of organs were in ‘general of 
the same size in all the adult animals examined. 
The muscle fibres and ganglion cells formed an exception to 
this rule. In Crepidula plana, the size of these cells was greater 
in the largest animals. This, he notes, agrees with the observations 
of Gaule, Donaldson, Hardesty, and Levi, who measured these 
cells in frogs and various mammals. In connection with the size 
differences found in these cells, Conklin cites the observation made 
by Levi, that these cells cease to divide early in life, whereas such 
cells as the epithelial and the gland cells, where Levi found no 
correlation with body size, continue to divide throughout life. 
The size of the sex cells, also, varied in the different species. 
In general, the smaller species produced larger eggs. These re- 
sulted in larger embryos, having larger cells. Conklin says the 
fact that the species with smaller eggs produce, in the end, larger 
adults, and that the final cell size is almost the same for all the 
crepidulas, is due to a longer duration and more rapid rate of cell 
growth and division in the larger species. 
A very notable case bearing on the question of the constancy 
of cell size in a species, is that of Oenothera gigas, a so-called mutant 
of Oenothera Lamarckiana, with double the number of chromo- 
somes found in the parent species. Gates (1909) found that the 
cells of Oenothera gigas, which have twenty-eight or twenty-nine 
chromosomes, were conspicuously larger than the cells of Oeno- 
thera Lamarckiana, whose chromosome number i is only fourteen. 
Boveri (1905), on the basis of extended studies on sea-urchin 
larvae, formulated the law that the cell size in sea-urchin larvae 
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