DEVELOPMENT OF A HYMENOPTEROUS PARASITE 543 
Two views are current regarding the nature of muscle attach- 
ments in Arthropods; the first according to which the muscles 
are inserted upon the chitin of the exoskeleton, is upheld by 
Snethlage (’05), Tower (’06), Holmgren (’02, ’07, ’10) and many 
others; the second according to which the muscles are attached 
to the hypodermal cells which often elaborate a fibrillar support- 
ing structure has found recent advocates in Maziarski (’03), 
Stamm (04), Henneguy (06), Wege (’11) and Torne (’11). 
Torne has shown in his very exhaustive contributions, with 
which my observations accord, that there are three definite types 
of muscle attachments in insects. The first type can be seen 
in the attachment of the mandibular muscle fibers of Dytiscus 
marginalis. Here the ‘indirect’ insertion of the muscles is very 
evident, the hypodermal cells on which they are inserted having 
definite and characteristic nuclei. The second type of which 
the muscles of the larva of Yponomeuta padi ZIl. are given as 
examples, shows the modified fibrillar structure of the hypoder- 
mal cells to which the muscles are attached. Many authors 
have used this type as evidence in support of the direct attach- 
ment of the muscles to the cuticula. A third type is seen in the 
wing muscles of many insects which show clearly that the muscles 
are inserted on the hypodermis. 
The larva of Spalangia, owing to its weak muscular develop- 
ment and small size, offers rather unfavorable material for the 
study of the subject under consideration. Sagittal sections 
stained with iron hematoxylin-eosin show clearly, however, that 
the muscles are attached to the hypodermal cells. In figure 14, 
it can be seen that the fibrillae within the hypodermal cells are 
devoid of cross-striations and are separated by a definite line 
from the muscle fibers. This line is continuous with the base- 
ment membrane, and evidently is a part of it. This is a good 
example of Térne’s second type of muscle attachment. 
The wing muscles in the late pupa of Spalangia offer a much 
clearer example of muscle insertion than is seen in the larva. 
Figure 15 shows the hypodermal cells at the point of muscle 
attachment greatly elongated and definitely separated from the 
muscle fibers by a distinct line, the basement membrane. The 
