118 GERM-CELL CYCLE IN ANIMALS 



attempts seem to justify the conclusion that the 

 division is equal or approximately equal, that is, 

 each group contains about thirty-two germ cells. 

 These groups acquire a covering of mesoderm cells, 

 are carried by the somatic tissues to a position 

 near the dorsal surface on either side of the body in 

 the last two abdominal segments, and thus become 

 germ glands situated in their definite positions. 

 Some time before the larval stage is reached, the 

 sex of the embryo can be determined by the shape 

 of the germ glands ; those of the male become dumb- 

 bell shape, whereas the female organs retain the earlier 

 pear shape and begin to acquire terminal filaments. 

 It is interesting to note that much time and 

 effort have been wasted by those who have attempted 

 to influence the sex of caterpillars by over-feeding 

 or starving. Kellogg (1907), for example, "dis- 

 covered," after an unsuccessful attempt to change the 

 sex of silk worms by this means, that these cater- 

 pillars already possess germ glands which are dif- 

 ferentiated as male or female. If he, and others 

 who have undertaken similar experiments, had 

 examined the literature on the origin of the germ 

 cells in insects, they would have found that as long 

 ago as 1815, Herold published results of investiga- 

 tions on Papilio brassica and other species of Lepi- 

 DOPTERA which proved that the sex of the larva is 

 already determined before it hatches from the egg. 

 A similar condition was reported in Bomhyx pint by 

 Suckow (1828), in Zeuzera oesculi by Bessels (1867), 

 and in Pieris brassica by Brandt (1878). 



