No. 2.] LARVA OF CTENOPHORA ANGUSTIPENNIS. 545 
The skin is very inelastic and tough, due to the deposit of the 
thick chitinous layer. The skin consists primarily of an irregu- 
larly curved layer of columnar epithelial cells, the hypodermis. 
This layer secretes the chitin, which is laid down in irregularly 
waved lamine. 
The muscle system is very complex and there are a great 
number of muscle bands. There is a wide band of longitudinal 
muscles along the side of the dorsal and ventral median line 
of the body. Some of the fibers reach from the exterior to the 
posterior border of each segment, but other fibers reach from 
the middle to either end, and still others reach from the mid- 
dle of one segment to the middle of another. There is also 
an inner set of lateral transverse muscles. Each muscle is 
a bundle of long fibers, each of which is enclosed in an outer 
elastic membrane, the sarcolemma. Each fiber is in turn made 
up of several fibrillae. The muscle fibers of the insect present 
a beautiful striated appearance, which is due to the alternate 
light and dark bands of substance. In life the muscles are 
colorless and transparent. They are so soft that they are of 
a gelatinous consistency. 
IV. MetuHops oF KILLING AND STAINING. 
Hot Gilson’s fluid was found to be the best reagent for 
killing the larve. With this the animals were killed very 
quickly and without contraction, while a slower reagent 
caused much distortion of the tissues. It was found impos- 
sible to make paraffin sections on account of the tearing of the 
rest of the section while cutting through the thick chitinous 
wall. Excellent preparations may be made by the celloidin 
method, although even here there is danger of tearing the 
inner delicate tissues. The best stain for use in making out 
the general differentiation of the tissues was found to be 
Bohmer’s. hematotoxylin. This stain was also used to good 
effect in working out the finer histological details, such as the 
cell structure of caecum, the finer details of the muscle struc- 
tures, and the details of the nervous system. Iron hematoxylin 
was found an especially good stain for working out the cell 
