3o8 BULLETIN OF THE BUREAU OF FISHERIES. 



granular, more deeply stained, oval in form, and are farther removed from the basement 

 membrane. Furthermore, large vesicular cavities occur within or between the cells 

 next the lumen of the glands, where products of nuclear degeneration are not wanting. 



It thus seems evident that the glandular epithelium of the oviducts pour an abundant 

 secretion over the eggs when these are delivered into the abdominal pouch. According 

 to the account of Scott quoted above, the eggs are viscous when they leave the ducts, 

 become adherent in sea water, but soon lose this property. So far as I have been able 

 to ascertain, eggs to all appearance ripe, which were taken directly from the ducts shortly 

 after egg laying, were nonadherent and showed no trace of cement or a secondary egg 

 membrane, but at this time the action of the glands had ceased. 



In the lobster with external eggs in segmentation, referred to above, the oviducts 

 were beaded with ripe eggs, or as Duvemoy expressed it, stuffed like sausages, with eggs 

 which failed of passage arranged in line, but they were not viscous at the time of exami- 

 nation, and were surrounded by the chorion only. Assuming that the oviduct contributes 

 to the formation of the cement, some other chemical products would seem to be needed 

 to render this effective. These are possibly supplied by the secretions of the tegumental 

 or "cement" glands of the swimmerets in the presence of sea water. At all events it 

 would seem that there is poured into the pouch at the time the eggs pass into it an abun- 

 dant milky or turbid secretion from these glands, which under the microscope is seen to 

 be swarming with minute floating particles or spherules. A similar secretion occurs in 

 the crayfish, which after the setting of the cement is found to cover her eggs in a sort 

 of protective "apron," as Andrews calls it, a sheet of grayish mucus or glair. When 

 this is removed the eggs appear bright and fresh beneath it. This "apron" seems to be 

 a residue of unused material, the presence of which may be needed not only to hold the 

 eggs and sperm in the pouch but to take part in the production of the liquid hydraulic 

 cement. 



COMPARISONS WITH THE OTHER CRUSTACEA, AND THEORIES OF HXATION. 



In the lobster the glue forms a thin transparent sac about each egg (fig. 5, pi. xliv 

 mV), and the capsules of adjoining ova are united by short solid ribbons, or flattened 

 strands of the same material. Similar bands adherent to the hairs and often coiled 

 spirally about them hold the entire egg mass to the body. The cement is thus a con- 

 tinuous sponge work, which is imitated in the manufacture of certain kinds of nut candy, 

 where the kernels are stirred in the thick sirup and held immersed when it hardens. 



Coutiere'' describes a slightly different mode of fixation in the Alpheidse (Alpheus 

 and Synalpheus), where the eggs or egg-groups adhere only to the stalk of the pleopods, 

 and never to the fifth pair of swimmerets, nor to the abdomen directly. The supporting 

 hairs are bunched at the two extremities of the basal stalk and are nonplumose, as in 

 the lobster. 



Where the eggs are few in number, as in Synalpheus longicarpus , they are glued 

 direct to the hairs, but where more numerous several hairs are cemented into a cable 



"Coutifere, H.: Les "Alpheidae," Morphologie externe et interne: Formes larvaires; Bionomie. Annales des Sciences 

 nattuelles, 8*= s6r., Zoologie, t. lx, p. i — ^rv, p. 428. 



