39 OTTO GLASER. 



for 2 hours to I volume of the standard secretion. If at the end 

 of this time the supernatant fluid is poured off and replaced by 

 fresh sea-water, free-swimming blastulae will be found within 24 

 hours. In one case only did development proceed to the pluteus 

 stage. 



Among the blastulse that develop in these cultures are some 

 characterized by an extremely slow rate of movement; others, 

 though rare, may move at a practically normal rate, whereas 

 the majority are considerably below normal in speed. This fact 

 in earlier expeiiments misled me, as I caught sight of only the 

 fastest swimmers, and mistook the otheis for arrested cleavages. 



The size of the blastulae is also a ready source of deception, 

 since there are in general three kinds, micro-blastulae, normal- 

 sized blastulse, and mega-blastulae, of which the first are by far 

 the most numerous. As these are usually very transparent and 

 also slow of movement their presence in a culture may easily be 

 overlooked. 



The origin of the micro-blastulse is clear. The first two cleav- 

 age cells, although normal in size, in most cases do not remain 

 together, but separate and proceed to develop independently of 

 one another. If the cells produced by these isolated blastomeres 

 continue to separate very minute micro-blastulae may result. 

 Such falling apart of the cleavage products has been observed in 

 the i6-cell stage and even later. The separation takes place, I 

 believe, because the fertilization membrane has not appeared 



('I3 1 ). 



Normal-sized blastulae need no explanation, since they must 

 result from the eggs whose cleavage cells can be seen to hold 

 together despite the absence of the normal fertilization membrane. 

 As for the mega-blastulae, it is possible that their origin is identical 

 with that of mega-blastulae in normal cultures. On the other 

 hand, they were more noticeable in the auto-parthenogenetic 

 series, and it is possible that the larger type of egg is better suited 

 for this than the normal mode of development. Again the 

 possibility is not excluded that the mega-blastulae may come 

 from eggs of normal size. This is not unlikely, since normal sized 

 blastulae instantly increase in volume when subjected to the 

 same concentrations of the secretion. 



