1888 - 89 .] Mr Irvine & Dr Woodhead on Carbonate of Lime. 329 
those parts which are essential for the procuring of food — the 
chelse or claws. 
It was interesting to watch the gradual deposition of carbonate 
of lime upon the membranous substance. At first widely separated 
points of calcareous matter (apparently spherical in form) were 
deposited ; these, widening from the nucleus, gradually formed 
into patches, which coalesced and ultimately became an unbroken 
surface of hard shell, consisting chiefly of carbonate of lime, which 
had been secreted from No. 2 water, although this water was 
absolutely devoid of that substance. The exo-skeleton thus formed 
was found on analysis to consist of carbonate and phosphate of 
lime and chitinous matter in the proportions present in normal 
shells. 
The washed mussel flesh upon which the animals were fed was 
found to contain traces of lime as phosphate, hut the total amount 
being less than 0‘08 per cent, (and although no doubt, like the hens 
the crabs could have elaborated carbonate from this phosphate), was 
too minute in amount to form a factor in the case, in the limited 
period required by it to form the new shell. 
All the three crabs confined in this No. 2 water cast successfully 
and formed calcareous envelopes, but ecdysis occurred so late in the 
season that in two of the three cases the animals had not vigour to 
complete the process, the cold retarding their powers to such an 
extent that before it was completed they sickened and died. This 
is in accordance with the fact that heat is a necessary element in 
the assimilation of lime salts from sea water by these animals, 
ecdysis only occurring during the summer months or in warm 
weather. 
Bromide of magnesium was added to a portion of the No. 2 water 
(see Appendix, No. 3 water), and a number of crabs and fish 
were placed in it. These all appeared to live in comfort, taking 
their food readily, and thriving, and we have no doubt that the 
same results would have been here obtained as with those already 
referred to, had the experiments been begun at an earlier period 
of the summer. Since this paper was read many other excellent 
examples of ecdysis, followed by complete shell formation within a 
few days, took place wfith crabs kept in the No. 3 water. 
At the suggestion of Dr John Gibson a fourth water was 
