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which at this stage forms by far the largest part of the claw rudiment, 

 is the neonychium. The eponychial layer of the epidermis still covers 

 the whole rudiment. (The thickness of this layer is exaggerated in 

 the figures.) 



By the stage shown in Fig. 4 the Krallenplatte is defined along 

 its whole length by its denser consistency compared with the rest of 

 the claw rudiment. It will be noticed from the figure that the 

 Krallenplatte has been differentiated out of the original claw rudiment 

 in such a way that its tip is embedded in the neonychium, which 

 forms a soft terminal cap of loose consistency in which but few fibres 

 have been laid down. Besides enclosing the point of the claw, the 

 neonychium extends underneath the whole length of the Krallensohle, 

 which however is easily distinguished from the neonychium by its 

 denser fibrillation. 



The neonychia at this stage are easily removed, leaving exposed 

 the claw proper (Krallenplatte and Krallensohle) and they are absent 

 in the next stage in my possession, a suckling young one still blind, 

 though evidently not quite newly born. It measures 19 cm, and its 

 claws are entirely of the strong sharp adult type (cf. Fig. 2), with no 

 traces of the neonychia. Having regard to the ease with which they 

 are removed in my oldest foetuses it seems extremely probable 

 that they are rubbed off by contact with the ground immediately 

 after birth, as will be seen to be the fate of the neonychia in the 

 chick. 



The foregoing description applies to the claws of the fore-limb. 

 The digits of the pes are also provided with neonychia, but they are 

 not so conspicuous, in correlation with the slighter development of 

 the claws here, which approach nails in appearance. 



The neonychium is thus a purely provisional embryonic appendage, 

 and it is extremely probable that its function is to protect the foetal 

 membranes from being torn by the claws during movements of the 

 embryo. As mentioned above, Tolypeutes has them developed to an 

 unusually great degree, and in this connection it is interesting to note 

 that it produces only one young one at a birth, and consequently the 

 full term foetus is comparatively large and strong. Moreover, the 

 short strong legs are not folded, but as can easily be seen in the 

 foetus in situ, the ends of the claws are actually in contact with the 

 chorion, and every movement of the limbs must draw them over it. 

 The neonychia provide exquisitely smooth, rounded surfaces for slipping 

 over the membranes with the minimum chance of tearing them. 



