1898.] APPEIfDAGES IN THE ABTHEOPODA. 931 



a more difficult matter to be sure as to the exact starting-point of 

 reproduction and the way in which the new growth is elaborated ; 

 for in these forms it does not project beyond the stump, and hence 

 it is visible only at the ecdysis which liberates it. [It is of interest 

 that the comparatively exposed condition of the new growth in 

 Crustacea is correlated with an aquatic habit, and its protected 

 condition with the terrestrial habit of the Tracheata ; though only a 

 bare suggestion that contact with hard surfaces, as on land, might 

 more readily injure a new and delicate structure is permissible.] 

 In the occluded condition of the new growth in Tracheates there 

 is necessarily involved a disturbance in the normal relations 

 between the chitinous investment of the stump and the subjacent 

 hypodermis. As development of the regenerated extremity 

 proceeds the hypodermis must slip away from the cuticle and 

 towards the base of the limb, leaving a space occupied by the 

 growing extremity. This structure is formed in a curled up 

 condition, and straightens only on libei-ation at ecdysis, as was 

 first described by Blackwall (3) in the case of Spiders. [Weismann 

 (78) has shown that in the normal development of Musca the leg- 

 rudiments are similarly curled up.] This state of things and the 

 displacement of the internal portions of the stump are illustrated 

 for Blattidse by figures 1 a and 1 h (Plate LVIII.). The regenerated 

 tarsus is curled up and occupies half of the chitinous stump of the 

 tibia, while the soft parts of the latter have largely withdrawn into 

 the chitinous femur. I have failed to make a satisfactoiy dissection 

 of the regenerated leg within the chitinous coxa and trochanter ; 

 but in such a case it would seem that the displacement of parts 

 must be more pronounced than in the case illusti-ated. 



It is obvious therefore that in Tracheata regeneration is com- 

 plicated by the peculiar occlusion of the new growth, and further 

 enquiry is necessary before we can say exactly what is the history 

 of the soft parts of the stump left by amputation, especially as it 

 is still uncertain whether normal ecdysis involves changes more 

 deeply seated than the mere renewal of the cuticle. If that is the 

 case, as seems suggested by such observations as those of Lubbock 

 (54) on the antennae of Chioeon and of Wagner (he. cit.) on Spiders, 

 there is no longer any question as to a "starting-point" of repro- 

 duction, for the new extremity would be a part of the general 

 reconstruction and not a bud. On the other hand, the elaboration 

 of the extremity as an outgrowth from the stump is certainly 

 suggested by the already mentioned observations of Newport on 

 Julus. It is, however, very possible that the phenomena of ecdysis 

 differ considerably in the several groups. 



The Eelative Size and Gteowth of Eepeoduced Appendages. 



The peculiar fact that it is a constant feature of reproduced 

 appendages in certain cases that they differ in structure from the 

 normal congenital appendages they replace wiU be dealt with later 

 on. At present only the size and growth of the regenerated 



