Page:Popular Science Monthly Volume 76.djvu/324

320 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:

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.

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."

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.

For example, a pair of A. fasciata, of which the wings measured, respectively, 46 and 48 mm. across, produced three specimens measuring only 36 to 39 mm., when the larval stage was reduced to 68 to 87 days, and the pupal to