330 Proceedings of Royal Society of Edinburgh. [sess. 
made up, chloride of calcium being substituted for sulphate of lime 
(carbonate of lime of course being excluded). This is referred to 
in Appendix as “Artificial Sea Water, No. 4.” Crabs placed in this 
water have lived during the past winter. We therefore presume 
that sulphate of lime is in no way necessary to maintain the lives of 
these animals. We also went a step towards determining the point 
as to what salts were absolutely necessary for the maintenance of 
marine life. A solution containing 2f per cent, of chloride of 
sodium in pure water (the amount present in normal sea water) was 
first prepared, and into this solution shore crabs were introduced, 
but after a few days, during which they refused to feed, they ail 
died. Chloride of magnesium was- then added to this solution in 
the proportion in which it occurs in sea water. In this mixture of the 
two salts, crabs and fish seem to live in comfort, feeding greedily, 
but of course ecdysis in such water was impossible. Chloride 
of calcium was added in amount equivalent to the lime in sea 
water, with similar results as regards the health of the animals ; 
but this was done too late in the season to allow of ecdysis taking 
place. 
§ 3. In accounting for the phenomena of ecdysis, some observers 
have asserted that crustaceans have reserves of calcareous matter in 
themselves, in the shape of abdominal and stomachical teeth “plates 
and stones,” from which they have the power of drawing supplies 
as they form their new calcareous structure. 
These gastroliths are undoubtedly the products of a regular 
epithelium just as much as is the carapace, and on careful examina- 
tion they are found to present the same microscopic structure.* 
These, along with the gastric armature, are thrown off into the 
cavity of the stomach, where they are dissolved, and whence they 
may be utilised for the very rapid deposition of a small quantity of 
the lime salts in the new chitinous covering. There is described a 
similar small reserve store in the lobster, in the form of small masses 
of rods composed of lime salts, .which at the time of the moult are 
thrown into the gastric cavity, where they lie until they are 
dissolved by the gastric juice. From analysis made it is evident 
that these reserves are, if they play any part at all, first converted 
* Max Braun, Arbeiten aus d. Zool. Zoot. Institut. in Wurzburg , 1875, 
vol. xi. pp. 144-489 ; Yitzou, Arch, de Biologic, vol. x., 1882, p. 659. 
