GERM CELLS OF ANURANS 275 
place at the stage when the chromosomes of Drosophila are 
known to be finely drawn-out threads. In other words, he local- 
izes the period of 'crossing-over' in the stage of oogenesis when 
twisting together of the homologous threads is possible. 
It matters httle, in so far as the validity of the genetical evi- 
dence is concerned, at exactly what stage in the germ-cell cycle 
'crossing-over' may take place, for that such a process does occur 
can scarcely be denied in view of the mass of positive evidence. 
It is not impossible that the phenomenon may take place at sev- 
eral different stages. 
It is an odd fact that 'crossing-over' of genetic factors appar- 
ently does not occur in the male Drosophila, but is confined 
solely to the female. Oddly enough, the chiasmatype theory 
invoked to explain it is based upon conditions observed in male 
Amphibia. So far no one has advanced a satisfactory explana- 
tion to account for the apparent absence of this phenomenon in 
the male Drosophila. Nabours has reported evidence for 'cross- 
ing-over' in the males of grouse locusts. Castle for the male rat, 
hence it is evident that it is not confined solely to females. 
4- The chromoplasts: {?) karyosomes 
Regarding the true nature of these bodies and their relation 
to the chromosomes, the writer is in doubt, Janssens ('05) 
who has made a- careful and detailed study of the origin and fate 
of these structures in Batracoseps states: 
Que le chromoplaste prend naissance aux derniers telophases sperma- 
togoniales et qu'il resulte d'un empatement du an depot d'une sub- 
stance siderophile entre les pointes des V chromosomes aux poles de la 
figure. 
Qu' a mesure que le chromosome se rempHt de substance siderophile 
le chromoplaste diminue de volume. II est done naturel de la con- 
siderer comme une substance destinee a etre absorbee par les chromo- 
somes a la fin du stade auxocytaire comme il semble qu'elle a etre 
excretee par eux au commencement de ce stade. 
This view is an interesting one; however, the writer has not 
paid sufficient attention to the chromoplasts and nucleoH in 
Rana catesbeiana to make any statement regarding the origin 
and fate of these structures. 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 32, NO. 2 
