THE MALE AND FEMALE EGGS OF PHYLLOX- 

 ERANS OF THE HICKORIES. 



T. II. MORGAN. 



The predetermination of sex in the egg has been demonstrated 

 only where small male and large female eggs occur, and it is a 

 very striking fact, so far overlooked I believe, that in these cases 

 the difference in the male and female eggs is connected with the 

 development of degenerate males. In Dinopliilns apatris the 

 male is smaller than the female, is degenerate, and the sexual 

 organs appear to be precociously developed. In Hydatina senta 

 the male is smaller than the female and degenerate. In the 

 Plivllo.vcra of the grape and of the hickories the male is small, 

 wingless, without digestive tract, and the sexual organs, as I shall 

 show for one species at least, develop very early, so that the 

 spermatozoa are fully formed before the male leaves the egg. 



In Dionpliilus it is believed that both the male and the female 

 eggs are fertilized, but in Hydatina and in the phylloxerans the 

 male and the female eggs are not fertilized. Sex in these cases 

 is, therefore, determined independently of fertilization and pre- 

 exists in the egg. In cases of this sort it would obviously be of 

 great interest to discover what conditions determine that some 



o 



eggs become males and others females. Is the difference, for ex- 

 ample, connected with a visible difference of the nucleus, or of 

 the cytoplasm ? This question I believe I am able to answer, but 

 the deeper-lying problem as to the causes that lead to the differ- 

 ence observable in the egg I have not fathomed. 



The material for study was collected from the galls of the 

 hickories in the spring and summer of last year, and included five 

 or six species, of which three only will be mentioned here. The 

 typical life history of these phylloxerans is the following : The 

 fertilized egg, attached to the bark, hatches in the spring pro- 

 ducing the stem-mother, who migrates to the young leaves and 

 attaches herself to one spot on the under surface of the leaf, 

 which becomes the center for the formation of a gall within which 

 she becomes enclosed. She lays a large number of eggs inside 



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