326 Proceedings of Royal Society of Edinburgh. [sess. 
the animals could not produce eggs with shells, the only protection 
to the egg proper being the strong membrane on which the 
calcareous covering or outer shell is, in ordinary circumstances, 
deposited. 
In each case these experiments were continued for about fourteen 
days, and between each change of such chemical feeding a course of 
carbonate of lime was administered, so as to bring the eggs again into 
a normal condition ( i.e ., eggs having true shells). We found it took 
about forty-eight hours for the hen to absorb and elaborate 
sufficient calcareous matter to reproduce the shell (after absorption of 
lime salts), and a similar period of lime starvation again to deprive 
the egg of its shell covering. 
The results of these experiments prove, beyond question, that egg- 
producing animals can form perfect eggs only when they have 
calcareous matter in the form of salts of lime in sufficient quantity 
present in their food, and that the lime salt found surrounding and 
protecting such eggs is generally carbonate, although this may, in 
some cases, be partly replaced by phosphate of lime. 
A series of experiments of a similar nature was made by Papillon 
(see Comptes rendus, vol. lxxi. p. 372), who “fed a pigeon and two 
white rats for two months on food containing phosphate of 
strontium, aluminium, and magnesium.” The ash from the bones of 
the pigeon was found to contain 8*45 per cent, of strontia, *66 
magnesia, and 6 - 95 alumina. H. Weiske-Proskau (Zeitschrift f. 
Biologie , vol. viii. p. 229) repeated these experiments, but failed to 
find the slightest trace of strontia or any noteworthy increase of 
magnesia. 
It is of interest to notice that as soon as these birds began to lay 
shell-less eggs, they contracted the habit of eating them. They 
were, at the conclusion of the experiments, perfectly healthy, the 
only noticeable point being that they were in excellent condition 
and very fat. 
If birds, then, can assimilate and secrete carbonate from other 
salts of lime, we consider we had strong ground for the statement 
we advanced in the first portion of our paper that coral animals 
could do the same thing, and we should have allowed this 
investigation to rest at this point. Mr George Brook proposed 
that we should continue these experiments with marine animals 
