NATURAI, history OP AMERICAN POBSTER. 
307 
The older writers, among whom were Cavolini (1787), Rathke (1840), and Brdl 
(1843), generally favored the first hypothesis. Lereboullet (i860) was the first to 
attribute the cement to the abdomen, and Braun (1875) the first to describe “cement 
glands” in the crayfish. Tegumental glands are found in practically every part of the 
body covered by the skin or invested by its folds, occurring even in the alimentary tract, 
the gills, seminal, receptacle, and the “ear sacs.” Feeding experiments with carmine 
seem to have shown that they have an excretory function in some degree at least, but 
it is equally certain that in some parts of the body they give rise to definite secretions. 
At the time of oviposition the pleopods of the female are swollen with what appears as 
an opaque whitish substance, which is seen upon microscopic examination to be com- 
posed of thousands of these organs. Each gland is hardly an eighth of a millimeter 
in diameter, and each opens to the exterior by a capillary duct, the entire length of 
which, not including the part which traverses the cuticle, is scarcely more than milli- 
meter and its diameter only y^-5 millimeter. Such organs are absent or found but 
sparingly in the pleopods of the male. After ovulation these glands appear to be for 
the most part in an exhausted condition, zymogen-like granules filling the central ends 
of their clustered cells. In one case examined, in which the animal had recently hatched 
eggs and was about to molt, the glands were shrunken and transparent. 
While these facts may be entirely misleading, an observation of Prentiss {2iy) seems 
to show that this is not the case, inasmuch as glands of this type occur in the sensory 
cushion of the otocyst of the crayfish and probably in that of all crustaceans in which 
sand particles are adherent to the sensory hairs. Until some more probable source of 
the secretion is discovered, it is reasonable to infer with Prentiss that these glands 
furnish the glue by which the otoliths are fastened to the pinnules of the sensory setae. 
THE OVIDUCT AND ITS PERIODIC CHANGES. 
The evidence regarding the part played by the epithelium of the oviducts will not 
be perfectly satisfactory until much more is known concerning the nature of the secre- 
tions of these organs during the period of egg laying. Our studies of the histological 
changes which the oviduct undergoes are limited to two significant stages, one in which 
the ovary was nearly ripe and the other from a female with external attached eggs in 
yolk segmentation. 
It is evident from a comparison of the critical stages that cyclical changes occur 
in the oviduct, no less marked in character than those which arise in the ovary itself, 
and to which they are evidently related. 
By the time the eggs are ready to be laid the oviducal epithelium is distinctly glandu- 
lar in type (fig. 3 and 4, pi. xlvii). Its cells become greatly elongated and distended, 
while after egg laying they are shrunken to less than one-fourth their former size. When 
treated with the common hardening and staining reagents before egg laying, the cyto- 
plasm is clear; the nuclei are also clear, elongated by the pressure exerted in the direction 
of the short axes of the cells, and lie well down toward the basement membrane. After 
ovulation the cytoplasm of the shrunken cells is more vesiculated; the nuclei are more 
62399°— Hr — II 
