490 A. B. DAWSON 
It is a pleasure to acknowledge here my deep indebtedness 
to Dr. H. W. Rand, at whose suggestion this research was under- 
taken and under whose helpful supervision it was carried out. 
I wish also to thank Dr. E. L. Mark, director of the Zoological 
Laboratory of the Museum of Comparative Zoology at Harvard 
College, for many privileges and courtesies extended to me. 
B. Material and methods 
The material studied was obtained from healthy animals sent 
to Cambridge from Venice, Ohio. All were full-grown with 
the exception of one larva 10 cm. long. 
Animals were either anaesthetized or killed in a 0.2 per cent 
solution of chloretone, which gave better results than either - 
chloroform or ether, since these reagents are very irritating and 
usually caused expulsion of considerable secretion. For the 
study of the glands most of the tissue was taken from the thin 
dorsal and ventral regions of the edges of the tail. This was 
advantageous for several reasons: first, because the glands are 
unusually well developed here; secondly, because little mechani- 
cal disturbance was necessary in removing a portion of integu- 
ment, and, thirdly, because the same animal could be used 
many times, as the surface exposed by cutting was very small. 
In fact, pieces were clipped from the tail of unanaesthetized 
animals without causing any apparent discomfort. Tissues 
obtained in this manner and fixed immediately permitted a study 
of the glands in a practically normal condition. 
Many common fixing fluids were used. Kleinenberg’s fluid 
gave the most satisfactory results, and a large proportion of the 
material sectioned was fixed in this way. Tissue so prepared 
did not become hard, took all stains readily, and the histological 
preservation was good. Bouin’s, Flemming’s (weak), Gilson’s, 
and Zenker’s fluids were employed occasionally. The granular 
secretion was best preserved by using a 2.5 per cent solution of 
formaldehyde or a saturated solution of corrosive sublimate. 
For microscopic study serial paraffin sections (10 u thick) were 
cut in two planes, one at right angles to, the other parallel to, 
the body surface. - Unstained preparations made from free-hand 
