III.] THE CO MM 02^1 FROG. 27 



of the gill-opening. Two others were dorsal spines 

 placed one behind the other on the mid-line of the 

 back. These poison-organs are probably only used 

 for defence. They are formed, however, on the very 

 same type as are the poison fangs of vipers. Unlike 

 the latter, however, they are not modified teeth, nor 



o. Fig. 9 



Fig. 8. — Vertical, Longitudinal Section of the Poison-fang of a Serpent (after 

 Owen). ^, deep groove ; o, its lower termination, which affords exit to the 

 poison ; p, pulp-cavity. Fig. 9. — Magnified Transverse Section of a Serpent's 

 Poison-fang (a'ter Owen), g, groove round which the substance of the tooth 

 (containing /, the pulp-cavity) is bent ; _/', the point where the sides of the 

 tooth meet and convert the " groove" into what is practically a ctntral cavity. 



are they situated within the mouth as they always 

 are in poisonous serpents. 



A Frog {Pelcbatcs fusciLs) which is comm.on in 

 France (and which is interesting on account of the 

 form of its skull hereafter to be pointed out), though 

 really harmless enough, has a singular power of 

 making itself offensive. 



Both males and females of this species utter a kind 

 of croak, and both, if the thigh is pinched, produce 

 a sound hke the mewing of a cat. At the same time 

 they emit a strong odour, which is like that of garlic, 

 and becomes stronger as the animals are more dis- 

 turbed. This emission not only affects the sense of 



