A contribution to our knowledge of the Stylopidae. 959 
General considerations. 
Although many of the details of the embryogeny are as yet quite 
unknown, it is very evident that there is a wide departure from the 
usual type of insect development, especially during the earlier stages. 
It is probable that the early differentiation of the primitive eggs and 
the way in which they are subsequently provided with yolk is cor- 
related with the parasitic habits of the adult female. Surrounded by 
food in great plenty, the ovaries as nutritive chambers become un- 
necessary, and the eggs migrate freely into the fat body. 
The very early stages present but little of especial interest, with 
the exception perhaps of the maturation phenomena. From my ob- 
servations it is seen that parthenogenesis occurs at least not unusu- 
ally, and I should not be surprised if it were the general rule. There 
is no arrangement for the spermatozoa to reach the eggs without 
passing through the epithelium closing the internal ends of the ovi- 
ducts and traversing a considerable part of the fat body. Copulation 
of some Stylopidae has been observed in some cases (SAGEMEHL, 1882), 
and it may be found that fertilization sometimes occurs. 
It is the stages immediately following the blastoderm which pre- 
sent the greatest difficulties of interpretation. I think it may be 
accepted that the hollow sphere of cells in its final form represents 
the germ band. But in this case, although derived from the cells of 
the blastoderm, it arises by neither of the typical methods: viz. by 
invagination or by the overgrowth of an amniotic fold. Apparently 
there is simply an irregular concrescence of the blastoderm cells at one 
pole of the egg, which are only later arranged to form the germ band. 
Its formation is thus necessarily a more or less discontinuous process. 
Certain of these stages resemble to some extent a number of figures 
which have been published of the embryos of some hymenopterous 
egg parasites, but these latter are so imperfectly known that it is 
useless to point out any resemblances. As no invagination or over- 
growth occurs in the formation of the germ band it is obvious that 
no amniotic or serosal membrane is developed. The later formation 
of secondary yolk is interesting as a similar phenomenon occurs among 
the Aphididae which like Xenos are viviparous. 
Post-embryonie Development. 
The first larval instar which is essentially a triungulin, is un- 
fortunately lacking in my material, but has been well described by 
