2o8 BUI<I,ETIN OP THE BUREAU OF FISHERIES. 



of the body, and which allowed these to glide smoothly over one another." The old 

 shell becomes brittle, owing to the absorption of organic matter previous to moltitig, 

 and if the carapace is pressed between the fingers it will sometimes split down the back 

 in the longitudinal median furrow, but in most cases the shell does not crack in this 

 plane unless artificially compressed. In the course of the preparation for the molt the 

 lime salts of the shell are absorbed along the middle line of the carapace, leaving a 

 narrow, perfectly straight gutter extending from the spine or rostrum to the posterior 

 margin of the shield. The chitinous portion of the cuticle still remains, forming an 

 elastic hinge, on which the lateral halves of the carapace bend without breaking asunder. 

 In the molted shell there is also a linear membranous area on either side of the rostrum. 

 Absorption of the hard matter of the shell at these points tends to give greater latitude 

 to the movements of the two halves of the carapace. If you examine a hard-shell lob- 

 ster, you will find in place of the median furrow a blue line, drawn as if with pen and 

 rule. Below this line the epidei'mic cells of the skin become so modified as to bring 

 about the total absorption of the lime salts of the cuticle. 



Other areas of absorption besides those of the great chelipeds, already described, 

 include the wide lateral margins of the gill covers or branchiostegites, which in life are 

 colored light blue, parts of the endophragmal skeleton, especially the roof of the pas- 

 sageway, in which are lodged the sternal blood sinus and part of the nerve cord, and 

 the endotergites, three small teethlike projections from the under side of the carapace, 

 on which the posterior gastric muscles are partly inserted. Rupture in the rostral 

 regions is further provided against by the narrow absorption areas on each side of it, 

 while the softening of the margins of the carapace makes the lifting of this from the 

 body an easy matter during the molt. The softening of the endotergites and apodemes 

 of the internal skeleton is also necessary to prevent injury to the soft tissues and to 

 permit their release. 



The lobster, as we have seen, leaves its old envelope by drawing the anterior part 

 of its body backward and the abdomen forward through a rent in the soft membrane 

 between carapace and tail. The cuticular lining of the masticatory stomach and esopha- 

 gus comes out by way of the mouth, while whatever is molted from the intestine is with- 

 drawn from the anus. The intestinal molt of the larva is apparently much more exten- 

 sive than that of the adult. When the discarded carapace falls back into its natural 

 position we might, as Reaumur says of the crayfish, mistake the empty shell for another 

 animal. 



THE GASTROLITHS, OR "STOMACH STONES." 



The gastroliths of Crustacea are found only in the lobster and crayfish, and according 

 to Patrick Browne, as noticed byStebbing {239), in certain land crabs of the island of 

 Jamaica. Having been first discovered in the common river crayfishes of Europe, 

 they figured in the old pharmacopoeias as oculi seu lapides cancrorum, and have excited 

 the interest of naturalists from early times. Owing to their transitory character, they 

 are not commonly seen in the lobster. 



