The Germ Cells of Diptera t,']'^ 



oogonial and spermatogonia! mitosis. In many cases the pro- 

 phases of spermatogonia and first spermatocytes resemble each 

 other very closely, the members of each pair being twisted 

 together in both. In the spermatocyte we get complete synapsis 

 and reduction; in the spermatogonium only a foreshadowing of 

 reduction, and abundant proof that synapsis is here a side-to-side 

 pairing of homologous chromosomes, and the first spermatocyte 

 division a separation of univalent chromosomes, and not a 

 longitudinal or quantitative division of two chromosomes united 

 end-to-end. The relation of the heterochromosomes to each other 

 in synapsis varies greatly with differences in form and size. 



One is tempted to suggest that if homologous maternal and pater- 

 nal chromosomes in the same cell ever exert any influence on each 

 other, such that it is manifest in the heredity of the offspring, 

 there is more opportunity for such influence in these flies than in 

 cases where pairing of homologous chromosomes occurs but once 

 in a generation. Possibly experiments in cross-breeding of flies 

 may bring out some interesting facts in heredity. 



Note. A preliminary statement in regard to the chromosomes of Drosophila 

 was made at the International Congress of Zoologists in Boston, August 21, 1907. 

 The question as to whether an odd chromosome or an unequal pair of heterochro- 

 mosomes was present in the male cells was then unsettled. 



LITERATURE CITED 



Boring, A. M., '07 — -A Study of the Spermatogenesis of Twenty-two Species of 



the Membracidae, Jassidae, Cercopidae and Fulgoridae. Jour. 



Exp. Z06I., vol. iv. 

 Castle, W. E., and others, '06 — The Effects of Inbreeding, Crossbreeding, and 



Selection upon the Fertility and Variability of Drosophila. 



Mus. Comp. Zool., Harvard, no. 177. 

 CuENOT, L., '99 — Sur la determination du sexe chez les animaux. Bull. Sci. de 



la France et Belg., vol. xxxii. 

 NowLiN, W. N., '06 — A Study of the Spermatogenesis of Coptocycla aurichalcea 



and Coptocycla guttata, with especial reference to the Problem 



of Sex Determination. Jour. Exp. Zool., vol. iii. 



