We have here a quite definite structural adaptation of the parts to a danger which often recurs--that of falling entirely into the power of an enemy which has seized the leg. By a sudden violent throwing-off of the leg the crab escapes from this danger. Quite similar adaptations are found among certain insects, such as the walking-stick insects or Phasmids, in which the mechanism is much the same, and lies at an almost exactly corresponding place, namely, at the line where the second and third joints of the leg, the 'trochanter' and the 'femur' meet. In this case the advantage of the arrangement is not merely that the animals are thus enabled to escape from enemies; it is useful in another connexion, for a knowledge of which we have to thank Bordage. This naturalist observed that the Phasmids not infrequently perished at one of their numerous moultings, by remaining partially fixed in the discarded husk. Of 100 Phasmids nine died in this way, twenty-two got free with the loss of one or more legs, and only sixty-nine survived the moult without any loss at all. That the moulting or ecdysis of insects is often hazardous may be observed in our own country, and it is familiar to every one who has reared caterpillars. These, too, often fail to get clear of their 'cast' cuticle, and they perish unless artificial aid is given to them. I have never observed any autotomy in them, but in the Phasmids it seems to be a much-used 'device' and is therefore of great importance in the persistence of the species. Limbs which are thus thrown off by autotomy regenerate again from the place at which they broke off, that is from the 'suture.' It had been noticed even by the earlier observers (e.g. Goodsir) that there was a jelly-like mass of cells within the joint, and that the development of the new limb started from this. It might be supposed that the regeneration-primordium is present in the rest of the leg also, but that is not the case, for the animal responds to the tearing off of one joint or of a smaller number than to the suture, not by regenerating the torn part directly, but by amputating the whole of the leg up to the suture, and then from this the regeneration of the whole leg takes place. In the Phasmids the case is similar, but with the difference that regeneration is possible from three places, from the tarsal joints, from the lower third of the tibia, and finally, from the suture between the femur and the trochanter. There is thus a regeneration-primordium (_Anlage_) at the beginning of the tarsal joints, another in the tibia, and a third in the 'suture' and the first must be equipped, as we should express it, with the determinants of the five tarsal joints, the second with those for the lower end of the tibia as well, and the third with all the determinants of the whole leg, from the 'suture' downwards.