LIMITS OF DIVISIBILITY or LIVING MATTER 329 



subjected to the same treatment with dilute sea- water as the 

 pieces which are about to be described. Fig. 80 is a double 

 embryo which had arisen from a bursted egg. The two 

 embryos are unequal in size, and the larger is ahead of the 

 smaller in development in so far as a deposition of needles of 

 calcium carbonate has 

 begun in the latter. 

 Both, however, are 

 less developed than 

 the pluteus which has 

 arisen from a whole 

 egg. Fig. 81 arose 

 from a fragment 

 which was smaller 

 than half the egg of 

 Fig. 73. It is an 

 early gastrula stage. 

 Figs. 82 and 83 are 

 still smaller frag- 

 ments of an egg, 

 which have, however, 

 reached only the bias- 

 tula stage. These ex- 

 amples are not 

 especially selected, 

 but they represent 

 only what the observ- 

 er will find in any sample from such a culture. 



Do these small pieces develop to the pluteus stage? Two 

 days later I found the conditions in this culture as shown in 

 Figs. 84-87. Fig. 84 is one of the smallest fragments living 

 at this time. It is only a blastula. Fig. 85 represents a 

 larger piece in the gastrula stage, but without any evidence 

 of a skeleton. Fig. 86 shows the smallest pluteus; Fig. 87, 



