THE GENETICS OF HABROBRACON JUGLANDIS ASHMEAD 



somes are lacking. Enough has been learned from 

 cytological observation, however, to make this 

 method of some value in connection with hatcha- 

 bility data. The chromosome aberrations ob- 

 served are necessarily gross ones and undoubt- 

 edly represent lethal effects in most cases. 



Unmated mature Habrobracon females, when 

 well-fed on host caterpillars and restrained 

 from ovipositing for several hours by removal 

 from host, store in each of their four egg sacs 

 from two to five fully mature eggs which may be 

 retained for at least thirty-six hours without 

 injury. After a much longer period of storage 

 they undergo resorption. They are all in late 

 irietaphase I with spindle attachment regions sep- 

 arated and about half way to the poles. The 

 ends of the dyads are still in contact so that 

 the chromosomes appear to be under tension. Oc- 

 casionally, an egg in late diakinesis or in ear- 

 ly metaphase I can be seen entering an egg sac. 

 Successively younger prophase oocytes occupy the 

 ovarioles anteriorly. Synapsis occurs as soon 

 as the youngest oocytes can be distinguished 

 from oogonia. An ovariole is represented sem- 

 idiagrammatically in Fig. 19. 



Dominant lethal effects are induced in all 

 eggs treated in metaphase I at about 1,000 R 

 units, in spermatozoa at 10,000 R units, and in 

 eggs treated in prophase I at 45,000 R units. 

 Spermatozoa are not actually inactivated by 

 doses much larger than 10,000 R units. Eggs are 

 also not inactivated by doses much larger than 

 lethal since they continue meiotic phenomena 

 under such conditions. These facts strongly 

 support the theory that the sex of the cell has 

 nothing to do with its response to X-rays but 



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