JO Edmund B. Wilson 



shown to be correct in principle by the work of Stevens and my- 

 self, that half the spermatozoa are male producing and half female 

 producing. This view rests on the following facts. When the 

 male somatic chromosome groups contain an odd number, includ- 

 ing an odd or unpaired idiochromosome (as in Anasa, Alydus, or 

 Protenor) the female groups have one more chromosome, being 

 duplicates of the male groups with the addition of another chro- 

 mosome like the unpaired one of the male. When the male groups 

 contain an even number, including a large and a small idiochro- 

 mosome (as in Lygaeus, Coenus or Tenebrio) the female groups 

 contain the same number, but include two large idiochromosomes 

 in place of a large and a small one. In the first type half the 

 spermatozoa receive the odd idiochromosome while half do 

 not, the former accordingly containing one chromosome more 

 than the latter. In the second type all the spermatozoa receive 

 the same number of chromosomes, but half receive the large 

 idiochromosome and half the small. It follows from these rela- 

 tions that eggs fertilized by spermatozoa containing the odd chro- 

 mosome, or its homologue the large idiochromosome, must pro- 

 duce females, those fertilized by the other spermatozoa males. 

 These cytological results, first reached by Stevens ('05) in Tene- 

 brio (which has a pair of unequal idiochromosomes in the male) 

 and myself ('o5b, 'o5c, '06) in Anasa, Protenor, Alydus and 

 Harmostes (which have an unpaired idiochromosome in the male) 

 and in Lygaeus, Coenus, Podisus and Euschistus (which agree 

 essentially with Tenebrio), have since been confirmed in a con- 

 siderable number of species and extended to several other orders 

 of insects. 2 They have recently received indirectly a striking 

 experimental confirmation in the important work of Correns ('07), 

 which proves that in the dioecious flowering plant, Bryonia dioica, 

 the pollen grains are likewise male determining and female deter- 

 mining in equal numbers. 



Gross's conclusion in the case of Syromastes and Pyrrochoris 

 is opposed to all these results in that only one of the two forms of 

 spermatozoa is supposed to be functional (those containing the 



a See the tabular review in the sequel. 



