348 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
The serial sections were cut 62 or 10m in thickness and stained on 
the slide. Borax carmine, safranin, haemalum, and several haematoxylin 
stains, including iron haematoxylin, were tried, but none gave as good 
results as a saturated aqueous solution of thionin. This is very selective 
and does not stain the cytoplasm of the growing tissues as deeply as 
most of the other stains. My thionin preparations have not faded 
much, though some of them are three years old. The preparations in 
which the stain has a greenish tinge fade more quickly than those in 
which it is of a deep blue. All of the preparations used in making 
drawings were stained in thionin. Haemalum and safranin are also 
very satisfactory stains. 
2. Histological Changes of the Muscles. 
The hypodermal muscles of insects exhibit three varieties which, 
though fundamentally alike, present quite different appearances under 
ordinary magnifications. Weismann (62) has designated these types 
as the larval, the leg, and the wing muscles, from their principal 
distributions. 
The muscles of the larval type include in Coleoptera not only all of 
the muscles of the larva, but also some of those of the pupae and 
imagines. Those found in the pupa and imago exist in the abdominal 
region only, and are muscles of the larva which have persisted unaltered 
during the metamorphosis. All of these muscles are composed of a few 
relatively large fibres with a well-marked sarcolemma, and usually with 
the nuclei at the periphery of the fibres. 
The muscles of the second, or leg, type are formed during pupal life, 
and are found not only in the legs but also in other parts of the body. 
In the imaginal form of Thymalus all of the skeletal muscles are of this 
type, except the few metathoracic muscles mentioned below, and the 
persistent larval muscles of the abdominal region noted above. These 
muscles are composed of numerous small fibres frequently arranged in a 
penniform or bipenniform manner and attached by a common tendon. 
The nuclei are found at the surface of the fibres in Thymalus, but in 
many other insects, including many Coleopterous forms, they are 
arranged in rows along the axis of the fibres. ; 
The muscles of the third, or wing, type are frequently spoken of as 
the fibrillar muscles, since they separate very readily into their primi- 
tive fibrillae. They are composed of very large fibres with nuclei scat- 
tered throughout their substance. Numerous tracheoles penetrate the 
fibres of these muscles. The following muscles are of this type in the 
