32 Mr. N. Annaiulale on some Oriental Geckos, 



dorsal surface lias a very close resemblance to lichen-covered 

 haik, aiul tliis rcsciiiblaucc is imu:li increased by the lajipet- 

 like ontgrowtlis on the tail and head. Hemidactylus pluty- 

 wus is certainly less conspicuous on a stone wall when its 

 lateral fold (wliich is not so very much less developed than 

 in Ptydiozoon, though this species does not " fly ") is spread 

 out on each bide oF it, as it commonly is. The same is 

 probably the case with Mimetozoon. It is possible also that 

 the folds in these forms have an adhesive function, as out- 

 growths on the tail have in some geckos ; but of this I have 

 no proof. On the whole, the attribution of powers of 

 " flight" to PtychozoonwovAA seem to be parallel to Cantor's 

 statement that Liolepis Bellii, a sand-loving, burrowing 

 Agaraid which very rarely climbs a tree, is in the habit 

 of " leaping from bough to bough." The foundation of 

 this statement was a real anatomical resemblance in 

 certain respects between Liolepis and Draco; but the loose 

 rib-supported membrane in the former has a totally diff'ereut 

 function from that of the latter, being used (partly, at any 

 rate) as a means of sexual display *. Similarity of structure, 

 even when it is pretty close, does not always argue similarity 

 of function. 



Note. 



While on the subject of " flying" quadrupeds, I take the 

 opportunity to restate in a clearer manner a remark recently 

 made about the "flying frog" {Rhacopkorus nigropalmatus, 

 Blgr.). In a note added to Mr. Eoulenger's " Report on the 

 Batrachians and Reptiles " in ^ Fasciculi Malayensis,'' Zoology, 

 vol. i. p. 138, I said: — ''Beyond the statement of the 

 Chinaman who procured Wallace his specimen, there appears 

 to be no evidence to prove that the 'flying frog' does use its 

 enormous feet to support it in the air, and, so far as we could 

 see, it did not appear likely, from the condition of the web 

 in the living animal, that their purpose was that assigned to 

 them by the discoverer of the species." By the condition of 

 the web I meant its flabbiness. It did not seem possible 

 that it could be rendered sufficiently rigid, and the frog made 

 no attempt to tauten it. Here we have a membrane provided 

 with skeletal supports, but probably only used as an organ 

 of adhesion. Gadow has pointed out how greatly the area of 

 the web was exaggerated in Wallace's figure (Gadow, Amphib. 

 Kept. p. 246, fig. 48; compare Boulenger, Fascic. Malay., 

 Zool. vol. i. pi. vi. fig. 1). 



* Annaiidale, V. Z. S. 1900, pp. 857, 858, and Fascic. Malay., Zool. 

 vol. i. p. 156. 



