NATURAI^ HISTORY OF AMERICAN I,OBSTER. 307 



The older writers, among whom were Cavolini (1787), Rathke (1840), and Erdl 

 (1843), generally favored the first hypothesis. I^erebouUet (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 ^vith 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 pleoppds 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 onlj' y^^ 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 (2x7) 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. xLvir). 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° — II II 



