A Sex-Intergrade Strain of Cladocera. 



3 



There would appear likewise no reason to assume that a so- 

 called neurotropic strain exists, but that in syphilis of the nervous 

 system the different forms of the Treponema pallidum may be 

 encountered. 



2 (1180) 



A sex-intergrade strain of Cladocera. 

 By Arthur M. Banta. 



[From the Station for Experimental Evolution, Cold Spring Harbor, 

 Long Island, N. Y.\ 



The above-mentioned strain appeared about a year ago. For 

 four years the writer had been breeding a number of strains of 

 Simocephalus vetulus. For 130 generations reproduction was 

 entirely parthenogenetic. The young were all females, there being 

 neither males nor sexual eggs. In the 131st generation of one 

 of the eleven strains of the species reared under laboratory condi- 

 tions for so long there suddenly appeared, in addition to normal 

 females, males and sex intergrades of many sorts. This strain 

 has continued to produce sex intergrades for a year — more than 

 twenty generations — and the character of the intergrades produced 

 does not seem different now from what it was when the sex inter- 

 grades first appeared. 



In this species, in addition to the character of the gonads, 

 eight morphological secondary sex characters are recognized. 

 In the sex-intergrade strain the sex array may be roughly classified 

 into normal females, female intergrades, hermaphrodites with 

 various combinations of male and female secondary sex characters, 

 male intergrades, and normal males. 



The female intergrades range from females with a single, 

 perhaps poorly developed, male secondary character to those 

 with all the secondary sex characters male. The hermaphrodites 

 have various combinations of male and female secondary char- 

 acters. There are male intergrades with as many as five secondary 

 sex characters, though ordinarily the male intergrades have only 

 one or two female characters. 



The male intergrades usually have incompletely developed 

 reproductive organs. Sperm is produced in various amounts. 



