EFFECT OF HEAT ON THE EGG OF CUMINGIA. 26l 



producing artificial parthenogenesis. A small flask of sea water 

 is partially immersed in a beaker of water, and warmed over a 

 flame. The eggs are put into this flask, and can easily be kept 

 at any desired temperature for an hour or more. The tempera- 

 ture most frequently used was that which had been most success- 

 ful in inducing parthenogenetic development, 32 to 34 C. The 

 length of the exposure was different, however, for while the un- 

 fertilized eggs are not injured by being kept at this temperature 

 for sixty, or even ninety minutes, the fertilized eggs appear more 

 sensitive and should not be heated for more than thirty-five or 

 forty minutes. In one series of experiments the eggs were placed 

 in the warm water within five minutes after insemination; in 

 the others they were watched until maturation was complete, 

 and transferred to the flask before the pronuclei had united. 



Eggs were preserved from the various experiments at different 

 intervals, and a large amount of normal material was also 

 preserved. Bouin's fluid was used as a fixative and the eggs were 

 embedded in paraffin in the usual way. The sections were cut 

 ten microns in thickness and stained with iron hematoxylin. 



III. Cytological Study. A few points in the normal and par- 

 thenogenetic development of Cumingia should be reviewed here 

 for the sake of clearness. The haploid number of chromosomes 

 is eighteen; they are very distinct in the first maturation spindle. 

 There is no reason to suppose that the exact diploid number is 

 not present in the first cleavage spindle of normally fertilized 

 eggs, but owing to the form of the chromosomes, accurate 

 counting is impossible. The long thin threads are so much inter- 

 twined, that individuals cannot be distinguished. In the par- 

 thenogenetic egg, however, the case is different. Here the chro- 

 mosomes of the first cleavage are small and very definite bodies- 

 and it is possible to count them. Since the chromatin of the 

 egg has not undergone reduction, one would expect to find thirty- 

 six chromosomes in the first cleavage. Such is not the case, 

 however; the number is variable, but always greater than thirty- 

 six. Fifty to sixty of these small masses of chromatin are present, 

 and it is evident that they do not represent individuals of the 

 normal chromosome group. Under the experimental conditions 

 a new distribution of the chromatic material has taken place, 



