DEVELOPMENT OF A HYMENOPTEROUS PARASITE 539 
case. However, it is not improbable that a considerable amount 
of oxygen is absorbed directly through the thin cuticula, a known 
method of respiration in Collembola. Howard (’92) has ex- 
pressed the view that oxygen is derived from the freshly aerated 
blood of the host which is ingested by the parasite. It may also 
be possible that a certain amount is liberated in a free state 
from the food during digestion in the mesenteron and that this 
is absorbed by the mesenteric epithelium. 
No trace of a dorsal vessel or other structures for the propul- 
sion of blood could be found. Such a system is quite unneces- 
sary because of the strong and apparently continual peristaltic 
body movements which, as stated above, were sufficient to move 
the adipocytes within the body cavity. 
The blood of Spalangia consists of a thin, colorless plasma in 
which float three types of cells, the leucocytes, the oenocytes 
and adipocytes. 
The leucocytes are small round cells with a central .nucleus 
and are of general distribution throughout the body cavity. My 
observations upon the oenocytes agree very closely with those 
of Weissenberg (’06) who worked upon the Chalcid parasite, 
Torymus nigricornis Boh. He found a larval and an imaginal 
generation of these cells, the former scattered about among the 
adipocytes without definite arrangement, while the latter, ap- 
pearing shortly before pupation, originated from the dorsal imag- 
inal discs on the fifth to the eleventh abdominal segments. Each 
group lay within a niche formed by the imaginal disc directly 
behind the developing stigma. During the pupal stage, the lar- 
val oenocytes underwent degeneration, their nuclei becoming 
crescentic and finally disintegrating. 
The larval oenocytes of Spalangia (fig. 10) are distributed 
generally throughout the body cavity, from the anterior end of 
the mesenteron to and including the region of the proctenteron. 
Often they are seen in disconnected groups near the developing 
tracheal invaginations; they may occur singly, in groups, or in 
rows of four or five among the adipocytes. They are oval or 
somewhat polyhedral in outline and vary from about 40 to 46un. 
in length. The cytoplasm is of a homogeneous structure, con- 
JOURNAL OF MORPHOLOGY, VOL. 24, No. 4 
