73 



At 3.00 P. M., on the 9tli, or two days and nineteen 

 hours after fertilization, owing to the increased amount 

 of water in the jar (I had by this time obtained a large 

 one,) and to the mortality among the embryos, I found it 

 very difficult to find any, and this difficulty was a con- 

 stantly increasing one thence forward. Those specimens 

 obtained had well developed shells, and the digestive 

 tract could be readily distinguished, as could the cilia. 

 The movements of the embryo were so rapid and erratic 

 that I found great difficulty in keeping them under the 

 high powder for a sufficient time to decide as to the stage 

 they had reached, but those least advanced aj^peared as 

 figured by Brooks, in No. 38, while the older embryos 

 presented the characteristics of figs. 39 and 42. 



At 11 P. M., on the 10th, or four days and three hours 

 after fertilization, the digestive tract and shells were 

 readily distinguished, especially the latter, which were 

 very apparent. The anus was observed in several cases 

 and the course of the intestine from it to the stomach 

 easily traced. The cilia of the velum was also apparent, 

 even with the low power. The main features at tliis time 

 were similar to those of figs. 42 and 44. 



At 11.00 P. M., on the 12tli, or six days and three 

 hours after fertilization, the embryo had apparently un- 

 dergone little or no change, except that a much larger 

 number had reached the stage shown in hgure 44. In 

 all, the shells and digestive organs were well developed 

 and apparent, and the movement of the cilia of the velum 

 regular and rapid, tliough the cilia appeared to have 

 decreased in size. 



At 11.00 P. M., on the 13th, se^en days and three liours 

 after fertilization, there was no ap])ai'ent change in those 

 embryos that could be found. They appeared quite 

 healthy and were rapid in their movements. The diffi- 

 culty of obtaining specimens, however, had mucli in- 

 creased. 



At 1 1.00 P. M., (m the 14th, eight days and tliree hours 



