tilting then the index finger and the little finger 

 toward himself, meanwhile separating slightly the 

 third and fourth digits, he will gain an idea from 

 his hand above the wrist, of the approximate ap- 

 pearance of the larval outline. The mouth of our 

 creature would be indicated by the space between 

 the first joint of the thumb and the palm, as seen 

 from above. 



That is to say, the mouths of my free-swimming 

 larvae were now at the top, considerably removed 

 from their original location in the early embryos. 

 Their bodies are no longer ciliated over the entire 

 surface, but a row of these rapidly vibrating lashes 

 extends along each of the four finger-like exten- 

 sions surrounding their mouths. These extensions 

 are supported by projections of the spicular skele- 

 ton, which in this stage has become quite complex. 



A few days later other extensions had grown 

 around the mouth, and my larvae had increased to 

 such size that their individual movements could 

 easily be watched with the unaided eye. Here and 

 there they swam, near the surface film of the water, 

 seeking the invisible notes of organic material that 

 served them as food. 



Then, shortly after, almost overnight, so it 



[107] 



