94 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
CHEMICAL ANALYSIS OF THE SHELL AND G ASTRO LITHS. 
It seemed to me that a chemical analysis of the shell of the lobster in its differ- 
ent conditions imposed by the molting habit might prove of interest, especially when 
compared with the composition of the gastroliths, and I am fortunate in being able to 
add as an appendix of this work the results of several analyses made by my friend, 
Professor Albert W. Smith. 
The most striking facts brought out by Professor Smith’s work are, first, that lime 
salts, carbonates and phosphates, form about half the constituents of the hard shell, 
there being from three to five times as much carbonate as phosphate. We also find 
that in the cast shell of the lobster, the brittleuess of which we have already noticed, 
the proportion of organic matter present is considerably less than under other condi- 
tions. An absorption of organic matter thus takes place during the period in which 
the new shell is formed, and this fact explains the fragility of the cast-off' shell. 
It is also interesting to notice that small quantities of alumina and silica are 
normally present in both the shell and gastrolith. 
The composition of the gastroliths is very like that of the shell, a conclusion 
which we would be led to draw from the fact that the gastrolith is but a specialized 
part of the dead cliitinous integument. The same substances are found in both, but 
in different proportions. The gastroliths are far richer in lime, chiefly in the form of 
carbonate (0aCO 3 ), than is the shell, and the amounts of magnesium carbonate 
(MgC0 3 ), alumina ( A1 2 0 3 ), ferric oxide (Fe 2 0 3 ), and silica (Sit) 2 ) are more or less reduced. 
Lime estimated as carbonate (Ca0O 3 ) constitutes about three-fourths of the 
gastrolith, but less than two-fifths of the carapace. Lime reckoned as phosphate 
(0a 3 (PO 4 ) 2 ) forms about 10 per cent of the gastrolith and but little less in the case of 
the shell; about 10 per cent of the gastrolith is water and organic matter, probably 
mainly chitin, and the rest is made up of the various salts and oxides given in the table. 
In the only molted shell analyzed about 38 per cent was water and organic matter, while 
in two hard-shell lobsters this percentage was considerably greater, 42.21 in one case 
and 51.80 in the other. 
The gastroliths of the crayfish were analyzed by Bulk ( 54 ) in 1834, 1 but apart from 
this rough determination no later work has been done ou this subject. 
He also analyzed the contents of the stomach of a crab newly molted, and found 
a free volatile acid, probably hydrochloric, present, besides lime salts ( 53 ). 
THE HARDENING OF THE NEW SHELL. 
Since the total quantity of lime contained in the gastroliths is insignificant com- 
pared with the amount necessary for building up the hard crust, the rapidity with 
which the new shell hardens depends, in some measure, upon the individual, and 
particularly upon the quality of its food. We have seen that the adolescent lobster, 
under 4 inches long, after molting swallows fragments of shells and other calcareous 
materials, which are dissolved in the stomach and help in strengthening the new shell. 
It is possible that older lobsters have the same habit. 
1 The results of Hulk’s work were as follows: 
Animal matter soluble in water 11. IS') 
Animal matter insoluble in water (probably chitin — Huxley) 4. 33 [ 
Phosphate of lime 18. 60 198. 93 
Carbonate of lime 63. 16 
Soda reckoned as carbonate 1. 41 J 
