GENETICS: A. M. BANT A 
375 
there would have been intergrades among their offspring if they had reproduced 
at all. 
Undoubted sex intergrades were first found and propagated in the writer's 
stock in one of the strains of Simocephalus vetulus. None have been seen 
in any strain of this species except in direct descendants of the initially discov- 
ered sex intergrade mother. Great numbers of Simocephalus vetulus have 
been examined microscopically especially in the last sixteen months and 
while normal males have been found on occasion, no sex intergrades have 
been discovered. This is true in spite of the fact that the sex characters are 
the characters especially scrutinized and that in the aggregate many thousands 
of Simocephalus vetulus have been examined. Hence in Simocephalus 
vetulus the occurrence of clearly marked sex intergrades is by no means to 
be considered a frequent phenomenon. 
In Daphnia longispina, however, sex intergrades have been discovered in 
all three of the strains of line 768, and we now have in the laboratory well 
established strains of sex intergrades from two of these three strains. Sex 
intergrades have been found also in two of the three other laboratory lines of 
this species. Coupled with the fact that the observation of probable sex 
intergrades at an earlier time was also in this species, the occurrence of sex 
intergrades in all except one of the six strains of Daphnia longispina in the 
laboratory, seems to indicate that for this species the production of sex inter- 
grade strains is not such an unusual phenomenon. However, one significant 
fact should not be overlooked, namely, that except for close scrutiny of the 
cultures including microscopic examination of great numbers of individuals 
the occurrence of intergrades would not have been suspected. 
Though in recent months males have been found in all except one strain of 
all the stock of the seven species of Cladocera reared in the laboratory no in- 
tergrades have been discovered in either Daphnia pulex, Simocephalus serru- 
latus, or in three species of Moina, or in Simocephalus vetulus except in de- 
scendants of the original sex intergrade mothers. The sexual characters of 
thousands of individuals of each of these species have been microscopically 
examined. 
Within the stock in the laboratory it then seems fairly clear that the oc- 
currence of sex intergrades is quite unusual, though intergrades have been 
found in most of the strains of Daphnia longispina. 
The sex intergrade strain of Simocephalus vetulus originated in October, 
1915, in line 740 in its 131st laboratory generation during a period of condi- 
tions of poor nutrition in the stock due to unsatisfactory food. 
The secondary sex characters and other matters relating to this intergrade 
strain have been discussed in some detail in another paper 5 (Banta, 1916) and 
need not be considered further here. 
The sex array is extensive. There occurs almost every combination of 
male and female primary and secondary sex characters. This coupled with 
the fact that most of the secondary sex characters occur very frequently in an 
