158 Miscellaneous. 



MISCELLANEOUS. 



Cement-glands and Origin of Egg-memhranes in the Lohster, 

 By Francis H. Heekick, of Adelbert College. 



The cement-glands have hitherto escaped detection in the lobster 

 {Homarus americanus)^ and consequentlj' the origia of the gluey 

 secretion in which the eggs are immersed at the time they are laid, 

 and by means of which they are attached to the body, has never 

 been accurately determined. 



Cano's valuable studies ("Morfologia dell' appareecio sessuale 

 feminile, glandole del cemento e fecondazione nei Crostacei Decapodi," 

 Mittheil. Neapel, Bd. ix.) have called attention to the much-neglected 

 cement-glands of the Decapod Crustacea. 



Erdl, in 1843, described three egg-membranes in the e^^ of the 

 lobster, and regarded the outermost of these as a secretion-product 

 of the oviduct. Bumpus also (' Journal of Morphology,' vol. v. 

 no. 2) attributes the " varnish-like layer," which surrounds the 

 ovum of Homarus at the time of oviposition, to a secretion which 

 probably comes from the columnar cells of the oviduct. Lereboullet 

 just escaped the discovery of the cement-glands in 1860, but cor- 

 rectly stated that the cement-substance came from beneath the skin 

 of the underside of the abdomen. The true cause of this secretion 

 was first recognized by Braun in 1875, and the subject has been 

 recently investigated in a large number of Decapods with great 

 clearness by Cano. 



When the lobster-embryo is about to hatch it is invested by three 

 membranes, from which it escapes to enter upon its first free- 

 swimming larval stage. The outermost of these is the membrane of 

 attachment. "Within this is the chorion, which is now nearly 

 absorbed. This is exceedingly delicate, and is often carried away 

 with the former in the process of hatching. The innermost mem- 

 brane does not belong to the egg, but to the embryo, which it closely 

 invests. The casting-off of this membrane forms the first moult, 

 and unless it is successfully thrown off the larva dies. The earlier 

 embryonic cuticles, which are formed in the long course of embryonic 

 life, are entirely absorbed at the time of hatching. 



The secondary egg-membrane, or membrane of attachment, com- 

 pletely separates from the chorion at the time of hatching, except 

 at one point, which is often opposite the thread-like stalk, with 

 which the outer capsule of the egg is continuous. The outer mem- 

 brane, which is less elastic than the chorion, is subjected to a high 

 degree of tension, until it finally bursts, splitting into two symme- 

 trical halves along the vertical longitudinal plane of the body of the 

 embryo, beginning at the liinder end and coming off over the head 

 and tip of the abdomen. 



When the chorion or primary egg-membrane is removed from the 



