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 

 gastrulaB five days old from the 

 culture under discussion. Fig. 90 

 is a smallest pluteus of the same 

 age. These gastrulse 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 



