ANIMAL PARTHENOGENESIS 49 



chromosomes are halved at each generation it is evident that 

 they must be doubled again somewhere during development. 

 In these cases where females result from parthenogenetic eggs, 

 the few observers 1 who have examined them agree in saying 

 that no reduction takes place ; there are two maturation divisions, 

 but in each the chromosomes split and their number is not 

 reduced. But there are other examples, of which the honey-bee 

 is typical, in which it seems that the egg may develop without 

 fertilisation, or may receive a spermatozoon and be fertilised. 

 Here there can be little doubt that normal reduction takes place, 

 and either the animal resulting from the unfertilised egg must 

 have half the normal number of chromosomes in each of its nuclei, 

 or a doubling must take place somewhere. It has been said 2 

 that in the bee such a doubling takes place, but more recent 

 work makes it probable that the statement is mistaken. For the 

 unfertilised egg of the bee yields a male, and in the spermato- 

 genesis of the drone one of the maturation divisions is sup- 

 pressed, 3 a fact which suggests that only half the normal number 

 of chromosomes is present. Also the number of chromosomes 

 at the end of the maturation is sixteen, while the observer who 

 stated that doubling took place in the unfertilised egg made the 

 reduced number (before doubling) eight. Probably, therefore, 

 he miscounted the number in the polar mitoses, and supposed 

 that doubling had occurred when he found sixteen in the later 

 divisions. 



A similar disagreement has arisen as to whether the chromo- 

 some number is restored to the normal (i.e. doubled) in cases 

 of artificial parthenogenesis. Most of such cases occur in eggs 

 which have undergone reduction, and the majority of observers 4 

 agree that the nuclei in the larvae produced still have the 

 reduced number. Others, 5 however, have maintained that the 

 normal number is restored. That restoration does not always 

 or even usually happen seems fairly clear, but instances have 

 been described 6 where a nuclear division has begun, and pro- 



1 Henking, Zeit. Wiss. Zoo. vol. liv. p. 147 ; Doncaster, Q.J.M.S. xlix. 1906, 

 p. 561. 



2 Petrunkewitsch, Zool. Jahrb. Anat. xiv. 1901, p. 573. 



3 Meves, Arch. Mikr. Anat. vol. lxx. 1907, p. 414. 



4 E.g. Wilson, Arch. Entwick. Mech. xii. p. 529. 



5 Delage, Arch. Zoo. Exp. et Gen. (3) ix. 1901, p. 301. 



6 Petrunkewitsch, Weismami Festschrift Zool. Jahrb. 1904, p. yy ; Kostanecki, 

 Arch. Mikr. Anat. lxiv. 1904, p. 1. 



4 



