377 



Occurrence of Neonychia in other Amniota. 

 I. M a 111 m a 1 i a. 



Neonychia occur in every order of unguiculate mammals. Through 

 the kindness of Mr. Oldfield Thomas I was able to look through a 

 few old foetuses of Rodentia, Insectivora, Carnivora and Cheiroptera 

 at the British Natural History Museum. The great majority of these 

 preserved specimens are provided with neonychia, though of a slightly 

 different type to that found in Tolypeutes. The point of the Krallen- 

 platte, instead of being embedded in the neonychium, fits closely 

 against it, as shown in the case of the chick (Figs. 5 and 7). A 

 reference to those figures will show that the presence of the neonychium 

 makes it quite impossible for the claw to scratch, as can be tested 

 ly drawing the claw over the skin. In foetuses nearly ready for 

 birth the neonychia are easily removed and if the claw is now drawn 

 over the skin it inflicts a sharp scratch. 



As examples of mammalian foetuses with neonychia of this nature 

 may be mentioned Trichys guentheri (Rodentia), Rhynchocyon sp. 

 (Insectivora), Proteles cristatus (Carnivora) and Pteropus edulis (Cheiro- 

 ptera), and very many others could be cited. I found a few cases 

 of well developed foetal claws unprotected by neonychia, but these 

 are almost certainly to be accounted for by the specimens having 

 been for a long time in alcohol. Even in fresh specimens near the 

 time of birth (judging from the case of the chick, — see below) the 

 neonychia are extremely easily detached, and in ripe foetuses that 

 have been preserved in alcohol they are often found to be missing 

 from several of the claws and though present in others, come off at 

 the slightest touch. In the few cases in which the neonychia were 

 altogether absent, they may safely be supposed to have been lost in 

 this way. 



Peculiarly shaped claw tips have been noticed by a few authors 

 in various mammalian foetuses. Göldi mentions the occurrence of 

 "hoof-shaped expansions" on the foetal claws of the rodents Coelo- 

 genys and Dasyprocta, and apparently also in Bradypus. Hausmann 

 who was mainly concerned with its histogenesis, describes and 

 figures the claw of a 9.5 cm foetus of Dasypus novemcinctus in which 

 the conditions are obviously closely similar to those in Tolypeutes. 

 His figure agrees in all essentials with my Fig. 3, representing 

 perhaps a slightly earlier stage. In the text he describes the 

 cylindrically drawn out point of the claw as enclosed in a cap of not 



