258 



GENETICS AND EUGENICS 



union of two gametes, the male is derived from a gamete 

 developing by itself. So far as chromosome constitution is 

 concerned, the female is duplex, the male simplex. 



In small Crustacea, and rotifers, the case is slightly differ- 

 ent. The female here, too, is duplex and the male simplex, 

 but the conditions of their origin are less simple, for the 

 mother here produces three different kinds of eggs. The first 

 kind never passes into the sunplex state of ordinary gametes, 

 but retains the duplex number of chromosomes, omits the 

 reducing cell-division, and begins development at once un- 

 fertilized and duplex. It forms a female, like the mother in 

 all respects. The other two types of eggs undergo reduction 

 and pass into the condition of gametes, with the simplex chro- 

 mosome mmiber. They differ in size. The smaller-sized egg 

 develops unfertilized into a male (simplex) individual, which 

 forms simplex sperm just as the male bee does, by omitting 

 a reduction division in spennatogenesis. The larger-sized egg 

 (winter egg) is incapable of further development without the 

 stimulus of fertilization. When fertilized, it develops into a 

 female individual, since in consequence of fertilization it con- 

 tains the duplex chromosome number. 



The cases of bee and rotifer agree in this, that the female 

 regularly has the duplex chromosome condition, the male the 

 simplex condition, a difference completely parallel with that 

 between Oenothera Lamarckiana (which has fourteen chro- 

 mosomes) and its mutant gigas (which has twenty-eight). 



In plant lice the difference between the sexes as regards 

 chromosome number is not so great. Here the female merely 

 has one or two chromosomes more than the male, recalling 

 the mutant Oenothera lata, which has one more chromosome 

 than the parent species, Lamarckiana. The male however 

 in plant lice develops from an unfertilized egg, partially re- 

 duced in chromosome number. The female arises either from 

 an egg unreduced and so with the full duplex number of 

 chromosomes, and which develops without fertilization into 

 a female, or from a reduced egg (a true gamete) which has 

 been fertilized and thus brought back to the duplex condition. 



