286 FRANZ SCHRADER 
to olygopyrene spermatozoa directly, while the other underwent 
an equation division and produced eupyrene spermatozoa. But 
such an explanation would rest on a very insecure basis, for the 
whole problem of abnormal sperm formation is still very much 
unsettled. 
The breeding experiments of Hindle (’17) with lice, Pediculus 
humanus, may be also mentioned here. Hindle obtained from 
single females broods consisting in some cases of both sexes, in 
others of males or females exclusively. Males were always put 
together with the females, but copulation was not observed, 
Hindle evidently assuming that this always took place. It 
seems to me that this is a fairly clear case of haploid parthenogene- 
sis.2. The fact that the same female in one instance produced 
consecutive broods of all males and all females seems to point to 
fertilization as the determining factor. Very probably the 
amount of sperm in the spermatheca determines whether females 
exclusively or a mixture of sexes is produced, while the entire 
absence of spermatozoa results in the production of males. 
Anthothrips verbasci, in which A. F. Shull (17) has found 
both sexes produced by fertilized females, and males only by 
virgins, no doubt also comes under the heading of haploid parthe- 
nogenesis. 
There are some cases where sexual eggs, capable of partheno- 
genesis, apparently develop with the diploid number of chromo- 
somes if unfertilized. The tick, Ambylomma dissimile, which is 
parasitic on Amphibia and reptiles, gives rise to females through 
parthenogenesis, while fertilized females produce both sexes 
(Bodkin, 718). The numbers given are too small to admit of 
any definite conclusion, but very probably parthenogenesis is 
diploid, and in fertilized eggs the spermatozoon influences polar 
body formation in some way. 
Very similar cases to this are found among the Orthoptera, a 
group in which the normal chromosomal behavior in the causa- 
tion of sex is well known, females being homozygous and males 
* Since the time of writing, K. Foote, Bio. Bull., vol. 37, and L. Doncaster and 
H. G. Gannon, Q. J. M.S., vol. 64, have investigated the cytology of Pediculus. 
Indications of a rudimentary division in spermatogenesis seem to confirm the 
above, but the chromosome counts are inconclusive. 
