THE AMERICAN LOBSTER. 127 



off from the rest of the cells. It should be remarked, however, that in two or three 

 days after ovulation (external eggs with segmented yolk) there is a striking lack of 

 uniformity in ,'ie condition of the glands, in many the central zymogen zone being 

 entirely absent. This may be due to the fact either that some of the glands recover 

 from exhaustion raster than others, or that they secrete unequally, or that some are 

 not roused to activity at all. 



Fig. 210, plate l!», is from the swimmeret of a female which had probably recently 

 hatched a brood and was close upon the point of shedding. As may be seen, the 

 glands are much shrunken in size, the cells transparent and non-granular, as if they 

 were completely exhausted. This seems to be a perfectly normal case, but whether 

 it has any significance in respect to the molt I am not able to say. 



HISTORICAL SKETCH OF THE CEMENT GLANDS. 



Cement glands have been described in numerous species of macrurous Crustacea, 

 but their structure seems to have been imperfectly made out. 



Oavolini, 1 according to Cauo {32), maintained that the cement came from the 

 oviduct, and Rathke {160) regarded the genital orgaus as the probable source of this 

 secretion. Erdl (63), in 1843, described three membranes in the egg of the lobster, 

 and considered the outermost of these to be the secreted product of the oviduct. 



Lereboullet {120) barely escaped the discovery of the cement glands of the crayfish 

 in 1860, but correctly stated that the cement substance came from beneath the skin 

 of the under side of the abdomen. He had indeed communicated this discovery to the 

 Natural History Society of Strasbourg in 1S52 (published in a note in L'Institut, 

 in 1853. See ref. 120.) As he says, zoologists had up to this time been almost mute 

 upon this subject, some explaining the attachment of the ova to an extension of the 

 primary egg membrane, others, like Milne Edwards {58), to an albuminous secretion 

 from the epithelium of the oviduct. Lereboullet described a milky-white matter rich 

 in fat and nuclei, which is present in the epiineral regions of the abdomen of the 

 female crayfish at the time of oviposition, but is not found in the male at any period 

 of the year. He supposed that this substance oozed through pores in the cuticle, 

 coagulated in the water after fixing the eggs, and that all trace of it subsequently 

 disappeared until the next reproductive period. 



The true source of this secretion was first recognized by Braun (22), who, in 

 1875, described cement glands in the crayfish. He showed that they consisted of 

 clusters of cells, which open to the surface of the abdominal appendages by narrow 

 ducts penetrating the cuticle — a single duct to each cluster. A little later {23) he 

 figured and described these glands in the six species of decapods. Similar structures 

 were found in the carapace aud oesophagus. GEsophageal glands (Speicheldrusen) had 

 been already seen in several species of crabs, such as Grapsus and Eriphia spinifrons, 

 and analogous structures were found in the labruin and maxilla?. 



Vitzou, whose work was published in 1882 {197), found glands generally present in 

 the oesophagus of all the crustacea examined, and they appear iu many of his drawiugs, 

 but no attempt seems to have been made to study their histology. The oesophageal 

 glands were extremely abundant in the lobster and Palinurus. The ducts are said to 



1 Memoria sulla geuerazione del pesci e dei granchi. Napoli, 1787. I have not had access to this 

 ■work, and quote it upon the authority of Cano. 



