No. 637] SHORTEE ABTICLES AND DISCUSSION 183 



are of this character. Certain connbinations, such as nine 

 females and one male, occur vdtYi very great frequency, sug- 

 gesting that a single male is produced at some definite point in 

 development. Statistical treatment of the data supports this 

 suggestion. My collea^e. Dr. Muller, has kindly calculated 

 the standard error and standard deviation of the numbers of 

 males per brood, and finds that they are 1.17 and .64 respec- 

 tively. These results show that the number of males produced 

 per brood does not vary as much as it would if males were 

 formed at random. If males weiT produced at random, the 

 amount of variation in the ni]m])er of males would be expressed 

 by a standard deviation of 1.17. This means that there is a 

 tendency to have the production of males confined to particular 

 cells in the embryonic mass, so that only one or two males are 

 usually formed in a brood. 



The fact that the parasite deposits one egg at each oviposition 

 makes it practically certain that the mixed brood of Platygaster 

 is the product of a single fertilized egg. The important ques- 

 tion is how the single male originates during the course of de- 

 velopment. I have elsewhere discussed this question, and have 

 suggested that the appearance of one or more males in a brood 

 may be due to an abnormal behavior of the sex chromosomes. 

 An abnormal division causing the loss of an x-chromosome from 

 one of the early blastomeres would explain the appearance of a 

 mixed brood, for such a cell could become the progenitor of one 

 or more males. 



J. T. Patterson 



