42 LOUIS AGASSIZ. 



than the air. . . . It is certain that the eggs 

 were already fecundated when we found them 

 in the ground, for later, I found several not so 

 far advanced as those you have, and yet after 

 three weeks I had tadpoles from them. In 

 those eggs which were in the lowest stage 

 of development (how they may be earlier, ne- 

 scio), nothing was clearly visible ; they were 

 simply little yellow balls. After some days, 

 two small dark spots were to be seen mark- 

 ing the position of the eyes, and a longitu- 

 dinal streak indicated the dorsal ridge. Pres- 

 ently everything became more distinct ; the 

 mouth and the nasal opening, the eyes and 

 the tail, which lay in a half circle around 

 the body; the skin was so transparent that 

 the beating of the heart and the blood in the 

 vessels could be easily distinguished ; the yolk 

 and the yolk sac were meanwhile sensibly di- 

 minished. The movements of the little ani- 

 mal were now quite perceptible, — they were 

 quick and by starts. After three or four 

 weeks the eggs were as large as peas; the 

 bags had burst at the spots where the eggs 

 were attached, and the little creatures filled 

 the egg envelopes completely. They moved 

 incessantly and very quickly. Now the fe- 

 male stripped off the eggs from her legs ; she 



