314 
THE PRINCIPLES OF 
Part II. 
With Siagonium (Staphylinidse), in which the males are furnished 
with horns, “ the females are far more numerous than the opposite 
sex.” Mr. Janson stated at the Entomological Society that the 
females of the bark-feeding Tomicus villosus are so common as to 
be a plague, whilst the males are so rare as to be hardly known. 
In other Orders, from unknown causes, but apparently in some in- 
stances owing to parthenogenesis, the males of certain species have 
never been discovered or are excessively rare, as with several of the 
'Oynipkhe . 67 In all the gall-making Cynipidm known to Mr. Walsh, 
the females are four or five times as numerous as the males ; and so 
it is, as he informs me, with the gall-making Cecidomyiim (Diptera). 
With some common species of Saw-flies (Tenthredinse) Mr. E. 
Smith has reared hundreds of specimens from larvse of all sizes, 
but has never reared a single male : on the other hand Curtis says , 68 
that with certain species (Athalia), bred by him, the males to the 
females were as six to one ; whilst exactly the reverse occurred with 
•the mature insects of the same species caught in the fields. W ith 
the Neuroptera, Mr. Walsh states that in many, but by no means 
in all, the species of the Odonatous groups (Ephemerina), there is a 
great overplus of males : in the genus Hetserina, also, the males are 
generally at least four times as numerous as the females. In certain 
species in the genus Gomphus the males are equally numerous, 
whilst in two other species, the females are twice or thrice as 
numerous as the males. In some European species of Psocus thou- 
sands of females may be collected without a single male, whilst 
with other species of the same genus both sexes are common . 69 In 
England, Mr. MacLachlan has captured hundreds of the female 
Ajpatania muliebris , but has never seen the male ; and of Boreus 
hyemalis only four or five males have been here seen . 70 With most 
of these species (excepting, as I have heard, with the Tenthredinse) 
there is no reason to suppose that the females are subject to parthe- 
nogenesis ; and thus we see how ignorant we are on the causes of the 
apparent discrepancy in the proportional numbers of the two sexes. 
In the other Classes of the Articulata I have been able to collect 
still less information. With Spiders, Mr. Blackwall, who has care- 
fully attended to this class during many years, writes to me that 
the males from their more erratic habits are more commonly seen, 
67 Walsh, in 4 The American Entomologist,’ vol. i. 1869, p. 103. F. Smith, 
* Record of Zoological Literature/ 1867, p. 328. 
68 ‘ Farm Insects/ p. 45-46. 
69 ‘Observations on N. American Neuroptera/ by H. Hagen and B. D. 
Walsh, ‘Proc. Ent. Soc. Philadelphia/ Oct. 1863, p. 168, 223, 239. 
70 ‘ Proc. Ent. Soc. London/ Feb. 17, 1868. 
