THE AMERICAN LOBSTER. 89 



[f the shell of a lobster which is nearly ready to molt is carefully removed, there 

 will be seen two glistening snow-white masses, one on either side of the stomach 

 (fig. 184, pi. 14, and cat 9, pi. C). The shape and dimensions of the gastrolith are 

 shown in cat 8 a-c, pi. 0. This particular one, from a, lobster 11 inches in length (No. 2> 

 table 24), was an inch long, three-quarters of an inch wide, and a quarter of an inch 

 thick. Its outer, convex side is applied to the sac in which it lies, while its concave 

 surface is separated from the cavity of the stomach by the old cnticnlar lining of this 

 organ (cut 9, pi. O). When the stomach is raised the gastroliths almost break through 

 its delicate outer wall by their own weight. They lie between the old cuticular lining 

 of the stomach, which may be stripped off, and its delicate outer wall, next the body 

 cavity. The impression of the gastrolithic plate is seen on the new cuticular lining 

 only (n. c. x ) If the sacs in which they are formed are cut open, each mass separates 

 into a large number — a thousand or more — of ossicles or columns. The majority of 

 these are slender, truncated prisms of irregular shapes, and 5 mm. or more long. 

 Each ossicle resembles a piece of milk-white glass, with transparent edges, and is 

 faintly marked with transverse and longitudinal striations, like those seen in the 

 cuticle (fig. 165, plate 42). 



On August 2. 1894, I examined a lobster which was very nearly ready to molt. 

 The old shell came off easily. The gastroliths were fully formed. We can detect upon 

 the new cuticular wall of the stomach the gastrolithic plate, from which the nest 

 gastrolith will be formed. When the old cuticular lining of the stomach is removed 

 the new teeth appear of the same brown color and nearly of the same hardness as the 

 old. The supporting calcareous parts are, however, quite soft. (For analysis of these 

 gastroliths, see No. 3a of table, Appendix II.) 



The gastrolith shown in its natural position in the sac (fig. 184, pi. 44) was from a 

 male lobster 7.5 inches long. This is the smallest animal in which I have found these 

 structures, and it is possible that they are not developed until the lobster is several 

 years old, although I have not obtained enough material to establish the time of their 

 first appearance with definiteness. A female lobster 3\\ inches long, which was taken 

 in Small Point Harbor, Maine, by Mr. M. B. Spinney, was as soft as wet paper, and had 

 apparently just molted. Upon dissecting this animal I was surprised to find the 

 stomach stuffed full of fragments of calcareous matter, consisting chiefly of waterworn 

 pieces of the shells of dead mollusks, such as are commonly thrown upon a beach. 

 The largest of these fragments was a quarter of an inch long. Many of the shells 

 were softened or corroded and were easily broken by needles. There were, besides, a 

 considerable number of small mollusks, such as the young stages of Mytilus edulis. 

 Some of these shells, when devoured, were undoubtedly alive. No trace of gastroliths 

 could be seen. The old cuticular skeleton of the stomach had been discarded, and the 

 new "teeth" were but little hardened, save upon their brown, horny surfaces. 



Another small lobster, a male, 4-^- inches long, taken at the same place and at 

 about the same time, had recently molted, probably within a few days. The shell was 

 very delicate and fragile. In this case, also, the stomach was loaded with fragments 

 of the dead shells of mollusks, crabs, and small lobsters. The hardest parts of the 

 shells of the latter seem to have been chosen, such as the stony mandibles, spines, and 

 teeth of the large claws. There was no fleshy substance which might serve as food in 

 this stomach. It is possible that these shells are swallowed by the young lobster, after 

 each molt, to furnish lime for the hardening of the cuticular skeleton. The absence of 



