42 PROF. J. ARTHUR THOMSON ON 
Phasmids, nine died during moulting, twenty-two tore 
themselves free with a loss of one or more legs, and only 
sixty-two survived without any loss. 
The most difficult case I know of is that of the abdominal 
appendages of hermit-crabs, which are normally protected 
by the borrowed shell. There are five—the first very 
rudimentary in males, but used for egg-carrying in the 
females; the fourth and fifth used for fixing to the shell. It 
is evident that all, especially the hindmost two pairs, are 
little liable to be nipped off. But Professor T. H. Morgan 
has shown that all the limbs are capable of regeneration, 
though they do not all grow again equally often, the anterior 
abdominal appendages being less frequently renewed than the 
more exposed thoracic limbs, though even these are not 
always restored after loss. He therefore concludes that 
there is here no relation between frequency of loss and 
regenerative capacity—a thesis which would be fatal to: 
Léssona’s law. Weismann’s general answer is that the 
regenerative capacity shown by the hermit-crab’s abdominal 
limbs may be a persistent inheritance from ancestral forms. 
with exposed tails. Morgan protests against this attempt 
to shunt the interpretation back to the shadowy past of 
possible ancestral history, but I do not myself see anything 
to complain of in Weismann’s argument. I should like, 
however, to enquire more particularly into the life of 
hermit-crabs to find out whether there are not now—in 
combats, in shifting from one shell to another, and particu- 
larly in moultings—some very good reasons for the per- 
sistence of regenerative capacity in these same hind legs. 
Another objection to the theory which interprets the 
occurrence of regenerative capacity as adaptive is found in 
those strange and highly interesting cases where the re- 
growth takes place, but not according to pattern. As. 
Spallanzani showed in 1768, and Morgan in 1899 (Anat. 
Anzeiger, xv. (1899), pp. 407-410. 9 figs.), a decapitated 
earthworm may grow a second tail (as shown by the direction 
of the nephridia) instead of replacing its lost head. But. 
this only serves to show that the regenerative machinery 
does not always work rightly. It confirms us in our belief 
that animals are by no means perfect in their adaptations. 
