THE AMERICAN LOBSTER. 93 



a lime reserve, it must be in the lymph, in the form of calcium phosphate, since they 

 have no gastroliths. "We think," they say, "that this theory [of the gastroliths 

 contributing to the formation of the new shell] may be dismissed as of comparatively 

 little importance, since, even if the teeth and whole calcareous structure could be 

 absorbed by the animals, the amount of carbonate of lime at their disposal from this 

 source is so small (a very small fraction of the outer covering) that it could not account 

 for any considerable part of the new structure. Consequently such an explanation 

 must be abandoned." 1 



These writers are undoubtedly right in attributing little importance to the gastro- 

 liths as a source of lime for the new shell. Lime is usually at hand in abundance in 

 the form of the dead skeletons of mollusks and other animals, and, as we have seen 

 (see p. 80), young lobsters make free use of it at the time of the molt. The fact that 

 the bracliyura have no gastroliths should also possess some significance. 



I have already shown that there are considerable areas in the shell where the lime 

 is completely absorbed preparatory to the molt. What becomes of the lime thus 

 removed ? So far as known, there is no means of eliminating it directly from the body, 

 and it is not likely that this amount of lime can be retained in the blood in addition to 

 that which the latter is constantly receiving from the food. It seems to me much more 

 probable that the gastroliths in the lobster represent the lime which has been removed 

 by absorption from the old shell preparatory to the molt, as well as, possibly, a small 

 amount which may have entered the blood from the food during the molting period. 

 The blood probably contains a maximum quantity of lime at this time, so that very 

 little can be absorbed from the food. Upon this hypothesis the absorption of the gas- 

 troliths is a purely secondary phenomenon and of comparatively little importance in 

 the vital economy. In the bracliyura, where no gastroliths are developed, we should 

 expect to find the absorption of lime from the shell to be relatively much less, which, 

 so far as I can ascertain, is the case. It seems to be a fact also that the absorption of 

 lime from the old shell proceeds pari passu with the growth of the gastroliths. 



Chantran observed (see p. 90) that when the formation of the stones was 

 arrested in the crayfish the animal died. This might be true of the lobster, and 

 would not conflict with the theory proposed. When once formed, the question of the 

 subsequent absorption of the gastroliths is not of vital importance. Vitzou speaks 

 of a lobster which died six days after the molt, without absorption of the gastroliths 

 having occurred. It would, of course, be very illogical to conclude that the gastroliths 

 were necessarily in any way concerned with the death of this animal. 



1 In an interesting letter from Dr. Irvine, describing some of his recent experiments, he says in 

 reference to a former attempt to determine the proportionate quantities of carbonate of lime in the 

 exoskeleton : "But as these experiments were made with the common shore crabs, containing much 

 less carbonate of lime proportionately to a full grown animal, I have repeated the determination, 

 using a full-sized lobster which weighed 15,000 grains. On carefully separating the stomach, and 

 freeing it from merely fleshy appendages and drying it, I find it to weigh about 50 grains or T gxy of 

 the whole animal, while the gastroliths weighed only 20 grains or yJ^ of the whole. I then carefully 

 dried the outer calcareous structure and found it to weigh 3,720 grains, the proportion between 

 the carbonate of lime in the gastroliths and in the outer structure being 20 grains to 3,720 gr ains 

 The CaCo 3 in the gastroliths thus stood in proportion to the CaCo 3 in the exoskeleton as 1 part in 186, 

 an amount too trifling to be of any practical service in providing calcareous matter for it." 



