330 STUDIES IN GENERAL PHYSIOLOGY 
a medium-sized pluteus which arose from a whole egg. If 
the linear dimensions of both plutei are compared, we find 
that they are about in the relation of one to two, which at 
equal density would correspond to a relation of their masses of 
one to eight. The smaller fragments generally do not go 
into a normal pluteus stage, but form only irregular needles 
of calcium salts, retaining, however, the spherical shape of 
the young gastrula. Figs. 88 and 89, for example, are such 
gastrule five days old from the 
culture under discussion. Fig. 90 
is a smallest pluteus of the same 
age. These gastrule with skeletal 
needles may grow, but their exter: 
FIG. 88 FIG. 89 FIG. 90 
nal form usually remains unchanged, and the skeleton remains 
abnormal. Finally, I should like to add a few words regard- 
ing the fate of such misshapen heaps of cells as shown in 
Fig. 76d. Their outer surface forms cilia, like that of nor- 
mal embryos, and like the latter they move with great 
rapidity in the aquarium; they seem to live as long as the 
plutei. These groups of cells represent free-swimming 
tumors, teratomas, which have arisen because of sliding 
motions of cells which could occur on a larger scale on 
account of the lack of a membrane. 
5. We have seen, therefore, that the smallest pluteus with 
normal shape which arose from a fragment of an egg had 
about one-eighth the volume of the normal average-sized 
pluteus which sprang from an entire egg. I may add that 
I have never observed smaller normal plutei than this. In 
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