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fully keratinised tissue (i. e. the ueonychium). 

 foetal stage of Dasypus claw described by him. 



This was the only 



II. Aves. 

 The condition of the neonychia in the chick, which is similar to 

 that most commonly found in mammals, is shown in Figs. 5 — 7. Fig. 5 

 shows a longitudinal section of a claw of a 19-day chick. The stain 

 used was borax-carmine ditferentiated for a few seconds in picric acid 

 in absolute alcohol. This method shows up the neonychia very plainly, 

 as owing to their sHght degree of keratinisation they are more strongly 

 stained by the carmine than by the picric acid, while the reverse is 

 the case with the other parts of the claw. 



Krallenplatte 



Krallenplatte 



Krallensohle 



Krallensohle 

 Fig. 5. 



Fig. 5. Median longitudinal section through the claw of a chick of 19 days 

 incubation. 



Fig. 6. Similar section, from a chick 12 hours after hatching. 



The relations of the neonychium to the other parts of the claw 

 are seen by a glance at the figure. Although it does not enclose the 

 point of the Krallenplatte as it does in Tolypeutes, it will be seen 

 that it fits closely into the concave side of the claw, thus turning the 

 point into a smooth rounded surface. It is easy to demonstrate by 

 experiment that the claw thus constituted slips over the allantois 

 without doing any damage, unless considerable force is used. If 

 however the neonychium is removed (which is very easily done at 

 the 19th or 20th day) and the claw is now drawn over the membranes, 

 it is found that it catches much more easily than before in the delicate 

 allantois, tearing it and thus causing bleeding^). 



1) I have purposely not gone into details as to the structure of 

 the neonychium, but it may be mentioned that in the chick the bulk 



