478 Alice M. Boring 



and the large one, maternal. In the second class, the odd chromo- 

 some is homologous with the large maternal element in the unequal 

 pair. The m-chromosomes are a pair, whose synapsis is delayed 

 until just before the first spermatocyte division. The third class 

 includes forms where there is neither an unequal pair, nor an odd 

 chromosome, and therefore no visible dimorphism of the sperma- 

 tozoa, but the fact that the equal heterochromosomes do not con- 

 jugate until after the first spermatocyte division, relates this class 

 to the first class, and suggests that there may be a masked dimor- 

 phism, the equal heterochromosomes representing different char- 

 acters, possibly, as truly as the unequal heterochromosomes where 

 there is a visible dimorphism. Wilson cites a great deal of evi- 

 dence for the individuality of the chromosomes, finding the same 

 size relations between pairs of spermatogonial chromosomes as 

 there are between single chromosomes in the spermatocytes. He 

 elaborates McClung's sex determination theory, brings forward 

 much evidence for the dimorphism of the spermatozoa, and shows 

 that there is a corresponding dimorphism in the somatic equatorial 

 plates of the male and female of several species of the Hemiptera 

 heteroptera. 



MATERIAL AND METHODS 



My material was collected at Woods Hole in the summer of 

 1905, at Cold Spring Harbor in the summer of 1906, and at Bryn 

 Mawr in the fall of 1906. The insects were caught in the usual 

 sweep net, and the testes dissected out as soon as possible. Each 

 testis consists of a group of several follicles, each attached by a 

 separate duct to the vas deferens. The testes from the larvae just 

 ready for metamorphosis, and from the adults soon after meta- 

 morphosis, in most cases give all stages from the spermatogonia 

 to the mature spermatozoa. 



Before putting up material of any species, Schneider's aceto- 

 carmine proved to be a quick and efficient reagent for determining 

 whether the testes contained all the important stages. This 

 fixes and stains the material at the same time. The testis is put 

 on a slide in a drop of the stain, and the cells separated by press- 

 ing down the coverglass. The preparation is made air-tight 



