i84 



CYTOLOGY 



CHAP. 



gigas. In the male meiosis of this hybrid, which has 21 chromosomes 

 (14 + 7), according to Geerts (1911), we get 7 bivalents and 7 univalents ; 

 i.e. of the triple set of chromosomes, two sets of homologues have paired, 

 leaving the other set free, as is probably also the case in Drosera. Gates, 

 however (1909 b), thinks it probable that there is no syndesis, and finds 

 that there are 21 univalents in metaphase I. (in the Oenotheras, the associa- 



FiG. 79. 



Side and polar views of the equatorial plate in the meiosis of certain Lepidoptera and their hybrids. (After 

 Federley, Z.A.V., 1913.) A, B, Pygaera anachorcla, 30 bivalents; C, D, P. curtula, 29 bivalents ; E, F", P. 

 anachoretaxP. curtula, hybrid; in E, 3 chromosomes are bivalent, the rest univalent; in F, 56 or 57 chromo- 

 somes can be seen, i.e. two or three are bivalent, the rest univalent. G, H, secondary hybrid obtained by 

 crossing the first hybrid back with P. anachoreta 9 ; in G a mixture of univalents and bivalents ; in H, 56 

 chromosomes can be counted ; namely, about 30 large bivalents (the anachoreta chromosomes), and about 

 26 small univalents {the curtula chromosomes). 



tion between the constituents of the bivalents in the meiotic division 

 is characteristically very loose). According to the latter authority these 

 21 chromosomes are separated at anaphase into groups of lo and ii, 

 rarely 9 and 12. According to Geerts the constituents of the bivalents 

 separate normally, sending 7 to each pole, while the remaining 7 uni- 

 valents suffer various fates — some being irregularly distributed to the 



