the formation of the crab-shell. This, however, is not the case in the formation of the egg-shell of birds. To quote de Varigny, page 202:
When laying hens are deprived of carbonate of lime by being shut into a room lined throughout with wood, without sand or soil, they are able to lay normal eggs, provided with the usual shell, if sulphate of lime is given them in their food. It follows that when the hen's organism does not receive carbonate of lime, as is usually the case, it is able to transform sulphate into carbonate.
De Varigny then says that other animals offer the reverse instance and alludes to the facts about the crab-shell, but does not see that this apparent contradiction is in any way associated with the great differences in organic complexity between the two animals, or that similar environmental changes have here produced a marked difference in the end product in the case of the lower creature and nothing in the case of the higher.
But these experiments are overshowed, and the great plasticity of this group of invertebrates is chiefly shown by the powers of regeneration which they possess. Experiments showing remarkable regenerative powers of the claws of lobsters, shrimps, crabs, crayfish, etc., are well known, and may be found described at length in any text-book dealing with the subject. In this respect they stand, according to Przibram, about on a level with the mollusks.
Insects
As soon as our review brings us to this highly differentiated group of invertebrates we see for the first time the fact that remarkable modifications are now chiefly associated with changes in the integument, especially changes of pigmentation. Profound modifications of a structural sort, and marked differences in body size are no longer met with.
We find, however, that changes in the surrounding temperature, and changes in food, affect the length of time occupied in the different stages of development of Lepidoptera; but in the end the result appears to be the same as under normal conditions. Morgan says: "The moth is identical with the normal," and at the end of his description of these experiments quotes the following: "What the insect gains in the larval stage it loses in the pupa stage."[1]
Some change in the size of the wings of the adult imago is another modification of an unimportant sort, and noted by Standfuss as a result of raising and lowering the external temperature during the larval period.
- ↑ "Experimental Zool.," p. 314.
