90 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



gastroliths may have no significance in these cases, but in order to determine this 

 one should examine the stomachs of larger animals which have recently molted under 

 natural conditions. 



The gastroliths, though a part of the cuticle, are not cast off during the molt, hut 

 are retained in the stomach. Wheu the old lining of this organ is withdrawn, the 

 gastroliths are soon set free, and breaking up into their constituent parts are speedily 

 dissolved. 



In the lobster referred to above (No. 2, table 24), which was preserved immediately 

 after the old shell was shed, the gastroliths were still in place in the stomach, and 

 unchanged. (For chemical analysis of these, see table, Appendix II, No. 4a.) The 

 horny parts of the gastric ossicles agree closely with those of the cast shell, having 

 the same light-brown color and approximately the same hardness. The supporting 

 calcareous parts are, however, quite soft. In every case which I have examined, the 

 old teeth are expelled from the stomach at the time of ecdysis, and not left with the 

 gastroliths, as Keaumur (161) said was true of the crayfish. 



Experiments upon the crayfish have seemed to show that the gastroliths are 

 necessary for the hardening of the new shell, but this is undoubtedly an error. 



The length of time required for the development of the gastroliths of the lobster 

 has not been determined. It is probable, however, that the latter part of their devel- 

 opment is rapid, and that they are conspicuous objects for a few days only before the 

 shell is cast off. 



A female lobster which was examined August 10, 1893, had a very hard, dull- 

 colored shell, which one might infer would be shed before many weeks. In place of 

 the gastrolith there was a very thin gastrolithic plate in the lateral wall of the stomach 

 (fig. 183, pi. 44). A section through this plate (fig. 171, pi. 43) shows how the gastrolith 

 is developed. The cuticular epithelium is columnar, consisting of very long, slender 

 cells. The thick excreted cuticular product is traversed by undulatory striations, 

 which mark off the columnar ossicles, the separation of which begins at the outer 

 surface. 



The inner section of the gastrolithic plate (G P) appears much more homogeneous 

 than the outer portion, although the demarcation is not quite so sharp as appears in 

 the figure. The striations in the inner part are only conventionally represented. The 

 undulatory striae extend inward, and with the deposition of lime the ossicles are 

 developed and completely separated. When the gastroliths are fully formed (cut 9, 

 plate (3) the deciduous cuticle of the gastrolithic sac is differentiated into two parts, 

 the gastrolith (gg) and a thin outer layer (oe\ cuts 9 and 10) corresponding to the 

 outermost part of the cuticle shown in figure 171 and in continuity with the old lining 

 of the stomach (Old G). The new cuticle of the stomach (New C) is represented in 

 the gastrolithic sac by a thin stratified layer (nc 1 , cuts 9, 11), from which the next 

 gastrolith will be developed. 



The condition of the gastrolith at this stage bears a resemblance to that which is 

 finally reached in the crayfish, where, according to Huxley (103) : 



It is a solid body which, in vertical section, is seen to he composed of thin superimposed layers, 

 the densest of which form the hard projections of the outer surface next the epithelial substratum. 



The outer side of the gastrolith in the crayfish is roughened with irregular promi- 

 nences, so that it resembles a "brainstone" coral. When from any cause the stones 

 are not dissolved, they lose their normal blue or white color and become brown or green ; 

 the shell remains soft and the animal, according to Ghantran, soon dies. When the 



