506 CHARLES ZELENY AND C. T. SENAY 



Plymouth Rock Fowl concerning which there is a controversy on 

 the cytological side. They are not included because they have 

 a special interest not connected with our main hypothesis and 

 because it is desirable to make at least one more series of meas- 

 urements in each species before publishing the data. Emphasis 

 is laid on the fact that all sets of measurements are published, 

 because bimodal distributions may appear occasionally as a 

 matter of chance in a uniform population. The frequency of 

 their occurrence is therefore all-important. 



The details of preparation of material and the method of 

 measurement are in all respects similar to those described by 

 Zeleny and Faust ('15 a) except that fixation was in all cases 

 in osmic fumes and staining in haematoxylin. The authors are 

 indebted to Mr. C. A. Hart for identification of the species. 



DATA 



1. Corizus lateralus, a hemipteran. The material was obtained 

 at the end of March and gave an abundance of active spermato- 

 zoa. Two sets of measurements, each of 500 spermatozoa, were 

 made. As shown in figures 1 and 2 the two determinations 

 agree closely. Each shows a pronounced bimodal curve with 

 modes at 27.1 m and 29.5 m, giving a ratio of 1.00 : 1.09. The 

 intermodal depression is deep and wide and the two elements 

 of the curve are approximately equal as regards number of indi- 

 viduals. There seems to be no doubt of the existence of two 

 distinct size groups with equal numbers of spermatozoa. 



The chromosomal history was worked out by Montgomery 

 ('06). He describes two kinds of spermatids, one with six and 

 the other with seven chromosomes. Two size groups are there- 

 fore to be expected but the drawings given by Montgomery 

 are not large enough to enable one to make a calculation of the 

 chromatin ratio. In Anasa tristis, another member of the Family 

 Coreidae, the expected ratio is 1.00 : 1.11. 



2. Leptocoris trivittatus, a hemipteran. The material was ob- 

 tained in early March and gave an abundance of active sper- 

 matozoa. Nine hundred and eighty-four measurements were 

 made. The frequency distribution as shown in figure 3 is some- 

 what irregular but there are two principal modes, one at 25.4 n 



