THE AMERICAN LOBSTER. 
89 
If 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. 44, and cut 9, pi. 0). The shape and dimensions of the gastrolith are 
shown in cut 8 a-c, pi. C. 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 tbe stomach by the old cuticular lining of this 
organ (cut 9, pi. C). When the stomach is raised the gastrolitlis almost break through 
its delicate outer Avail 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. 1 ) 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, Avith 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 gastrolitlis were fully formed. We can detect upon 
the new cuticular wall of the stomach the gastrolithic plate, from which the next 
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 
gastrolitlis, see No. 3 a of table, Appendix II.) 
The gastrolith shown in its natural position in the sac (fig. 184, pi. 44) Avas 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 3y^ inches long, Avliich 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 Avaterworn 
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, Avere undoubtedly alive. No trace of gastroliths 
could be seen. The old cuticular skeleton of the stomach had been discarded, and the 
new “teeth” Avere 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, sucb 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 
