88 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



natural position one might, at the first glance, as Reaumur said of the crayfish, mis- 

 take the empty shell for another lobster. 



In old lobsters, where the membranes are thick, a rupture of the carapa.ce may 

 arise possibly from want of complete absorption of the lime, but this rarely happens, 

 and the lobster gains nothing from the complete dehiscence of the parts. 



It has been stated so many times that it has come to be generally believed — the 

 result of the reiteration of error — that the carapace of the lobster is ruptured along 

 the middle line to assist ecdysis. A careful examination of the cast-off shell, which 

 would have settled in short order the disputes over this subject, is the very thing 

 which apparently has not occurred to anyone to make. Wbeu this is done, we find 

 that rupture of the shell is guarded against in the most ingenious way. The areas of 

 absorption of lime salts in the carapace, which we have only to consider in this 

 connection, are as follows : (1) The wide lateral margins of the branchiostegites, 

 including what in life appears as a light blue area, about three-eighths of an inch wide 

 in a lobster 10 inches long; (2) a narrow median stripe extending from near the apex 

 of the rostrum to the posterior margin of the carapace; (3) the endotergites (three 

 small teeth like projections from the under side of the carapace, on which muscles are 

 inserted); (4) a linear area on each side of the rostrum ; (5) two small round areas in 

 front of the endotergites — not always noticeable. The linear area (2) extending down 

 the back acts as a hinge, rupture in the rostral region being provided against by the 

 narrow absorption areas on each side of it (4), while the softening of the margins of 

 the carapace makes the lifting of this from the body an easy matter during the molt. 

 The result of such areas of absorption is plainly to prevent the rupture of the shell, 

 which, however, does accidentally occur from other causes. The softening of the endo- 

 tergites is also necessary to prevent injury to the soft tissues. 



THE GASTROLITHS. 

 THE GASTROLITHS OF THE LOBSTER; THEIR STRUCTURE AND DEVELOPMENT. 



The gastroliths, though often called crabs' eyes, are found only in the crayfish and 

 lobster, so far as is known. Discovered first in the river crayfishes, they early figured 

 in the old pharmacopoeia as oculi seu lapides cancrorum, and have excited the interest 

 of naturalists from early times. Owing, however, to their very transitory nature, they 

 have been generally overlooked in the lobster. A satisfactory explanation of the 

 function of the gastroliths has, in my opinion, never been given, and in the following 

 section I shall offer one which I think is in harmony with the facts. 



The first reference to these bodies, which I have found, is by Greoffroy the younger, 

 in 1709 (74), who says, in his paper on the molting of the crayfish: 



Although I have spoken only of the stones which are found in the river crayfish, there is, more- 

 over, a kind of crayfish, called Astacus marinus, in French Ho mar, in which they also occur. 



More particular reference was made to them in 1874 by Chantran (41), and they 

 are mentioned for the first time in the American lobster by Wheildou in 1875 (202), 

 who says that "just before shedding a white substance, the size of a 5-cent coin, is found 

 on either side of the stomach. These bodies harden into limestone and are absorbed 

 in the process of forming the new shell." They are described by Vitzou (197) as an 

 inorganic reserve composed of small truncated rods, free or delicately bound together. 



