71 



eggs examined had passed through the first stage of 

 activity, and as far as could be decided had reached the 

 second period of rest — resembling Brook's hgs. 8, 9 and 

 10. I was called away from the microscope at this time 

 and was unable to trace the changes during the second 

 period of rest or to note the time of fcheir occurrence. 



At 1.27 A. M., or five hours and fifteen minutes after 

 fertilization, the eggs had j)assed through the second 

 period of activity and had entered upon the third period 

 of rest. In some of them the four micromeres were 

 easily observed, but in others they were not so distinct ; 

 a few were as figured by Brook's (fig. 16), but the ma- 

 jority appeared as in figs. 18 and 19. 



I was unable to follow the intermediate changes be- 

 tween those of the third period of rest and those of the 

 first swimming stage, but at my next observation, at 4.30 

 A. M., on the 7th, larger nuinbers of eggs had reached 

 the latter stage and were swimming at the surface of the 

 water. The cilia were well developed and the movements 

 of the embryo very rapid — their appearance Avas exactly 

 as figured by Brooks' figs., 32, 33, 34 and 35. The water 

 in the glass was now siphoned oif, into a jar, that the 

 embryo might have room for development and be free 

 from the influence of decaying eggs ; but as I had but 

 two fruit jars holding a quart each, witli which to con- 

 duct my experiment, I was forced to take many eggs into 

 the second receptacle before they had developed swim- 

 ming powers, or else sacrifice them. As the rate of seg- 

 mentation was very irregular, I had for a time, what Avas 

 to me, a rather confusing mixture of eggs in the process 

 of segmentation and developing embryos ; l)ut with care 

 and close observation, I manaoied to follow each lot until 

 they reached tlie swimming stage and could observe no 

 difference between them and tlie first, except in the rate 

 of change from one period to another. 



At 12.30 P. M., June 7th, or sixteen and a-half hours 

 after fertilization, there were many eggs in the first swim- 



