554 



MR. D, W. DEVANESEN ON THE 



in relation to the lymphatic septa, the latter are probably 

 deposited in connection with the peritoneal membrane. Their 

 function, as has been ascertained, is to assist in the general 

 metabolism of the body during aestivation. 



(3) The stoutness of this toad is, in the first instance, due to 

 the enormously developed viscera. This condition is improved 

 upon by the inclusion of a part of the thigh into the contour of 

 the trunk and by the enlarged sub-cutaneous lymph-sinuses. 



(4) In the skeleton the vestigial state of several of the bones 

 of the head is remarkable. This and the consequent engysto- 

 matous mouth are, in my opinion, related in some unknown 

 manner to the nature of the diet, which consists almost entirely 

 of termites*, winged or wingless according to the season. 

 Witness, in this connection, the similar efi"ect produced by a 

 similar diet on the Myrmecophagidse among Mammals. 



(5) It is noteworthy that the pre-hallux of Rana, usually 

 regarded as a degenerate digit, has in this toad become an organ 

 with a definite function, viz. the so-called " inner metatarsal 

 tubercle." 



(6) While certain muscles, for example the sterno-radialis and 

 the deltoideus, show a remarkable degeneration, other muscles, 

 for instance the muscles of the hyoid a,nd of the floor of the 

 mouth, exhibit an equally remarkable specialisation. The 

 muscles examined also show important diff"erences in their rela- 

 tive dimensions, origins, and insertions. Certain new muscles 

 are present which have been already described, while three 

 muscles are absent, viz. the cutcmeus-pectoris, omo-hyoid, and the 

 rectus-femoris-anticus. Again, certain non-cutaneous muscles of 

 Eana have acquired a partial connection with the skin, for 

 example, the rectus-intei-nus and the portio-ahdominis. Assuming 

 the muscular anatomy of Rana to be typical of the Anura, one 

 may trace the difierences in the musculature of this toad to two 

 factors, viz, the fossoi-ial habit and the nature of its food. This 

 creature passes the greater part of its life underground, seeking 

 water only for breeding purposes. This implies that, while the 

 same muscles called into frequent activity in an aquatic frog 

 may sufifer by the want of regular use, other muscles of a direct 

 utility in burrowing are likely to be improved and exaggerated. 

 At the same time, the curiously specialised muscles of the hyoid 

 and of the floor of the mouth probably indicate a more efticient 

 method of capturing insects. 



(7) Beddard (1) mentions three characters which may be 

 common to the Engystomatidae : these are (1) the partially cuta- 

 neous origin of the 7-eGtus-internus-minor , the specialisation of 

 the muscles of the floor of the mouth, and the division of the 

 " outer portion of the sternohyoideusr One may say that in 



* AlthoTigli it is true that insects form the chief food of frogs in general, j^et a 

 liberal diet of termites alone appears to prodnce the peculiar effect on the consti- 

 tution which we have indicated. 



