628 



Chas. B. Wilson 



Samples of each kind of eggs were placed in four different 

 solutions, viz. 



1. KiNGER solution undiluted. 



2. - - diluted one third with water. 



3. - - - - half. 



4. - - - two thirds. 



The results obtained from the eggs in advanced stages of 

 development can be considered more appropriately later, and we will 

 concern ourselves here with the experiments upon unsegmented eggs 

 (Rana) only. 



Most of the eggs were left in the jelly as they were found 

 except that the bunches were divided once or twice to reduce the 

 bulk. Some of them, however, were removed from the egg membranes 

 and placed in the solution entirely free. These developed as far as 

 the closing of the neural folds and then all quickly died. By com- 

 paring this result with that obtained in salt solution, it seems reason- 

 able to suppose that the closing of the neural folds represents a 

 critical period in the development of these embryos. 



Such a conclusion is strengthened by the following facts. In 

 every bunch of eggs there is considerable difference in the rate of 

 development. Some eggs reach the stage just mentioned sooner than 

 others. These were usually the first to die, while those that developed 

 more slowly lived until they reached the same stage. Thus the 

 deaths were not simultaneous, but they did all take place at about 

 the same development period. 



Furthermore the very thing occurred which would be naturally 

 expected-viz. a few eggs produced embryos more vigorous than the 

 rest, and these developed for two or three days beyond the closing 

 of the folds, and then gradually weakened and died. In every in- 

 stance there was no more than the average loss previous to this 

 stage. There must be something, therefore, nearly simultaneous with 

 the closing of the neural folds, which renders this particular period 

 fatal to embryos deprived of the protection afforded by the egg 

 membranes. This something appears to be the: 



Ciliation of the Larva. 

 This was first recognized by Claeke in '80, but has been 

 doubted or entirely overlooked by others. Very recently (Feb. '96) 

 AssHETON (2) has worked out the ciliation of Rana temporaria, and 



