48 ON SOUTH AFRICAN CHAMELEONS, ETC. 



This appears to be a most interesting adaptation — a dynamic manifestation 

 of the principle discovered in its static form by Mr. Abbott H. Thayer. 

 Mr. Thayer first suggested that the relative shades of the dark back, lighter 

 sides, and white under sides of animals were such as just to counterbalance 

 the diminution of natural illumination from an open sky as we pass from the 

 back down the sides to the under surface ; that the object of this counter- 

 grading was to neutralise the shadow w^hich would otherwise render the 

 animal conspicuous. C. pumihis, as I have said, manifests the same principle 

 in a dynamic form. The side that happens to be turned away from 

 the light is brightened sufficiently to neutralise the shadow ; the high 

 illumination of the other side is toned down by darkening, the effect being 

 that all appearance of solidity is dissipated. This result must be of great 

 importance to so large and so defenceless an animal as the chamseleon. But 

 for this adjustable countergrading, the varying degrees of illumination on the 

 side and dorsal slope turned towards the light, combined with the strong- 

 shadow on the other side, would cause it to stand out among the leaves as an 

 object of conspicuous solidity and thickness. 



5. JS^ote on the Vitality of the Tail of a South African Gecko, Pachydactylus 

 MACULATUS, A. Smith. By Dr. Gr. B. Longstaff. 



The Gecko on which the following observations w^ere made was found 

 under a stone on Hlangwana Hill, Colenso, 24th August, 1905. 



Sluggish ; eyes large. Body dull pale brown, with a conspicuous row of 

 dark brown spots on either side of the back, outlined with black and outside 

 that with pale ashy ; belly flesh-colour. 



When chloroformed, the short stumpy tail was cast off (causing slight 

 hEemorrhage) , and took much longer to die than the body, wa-iggling with a 

 spiral movement. 



[The vitality and activity of the tails of lizard.s after they have been cast off are, I believe, 

 an adaptation for the purpose of aiding' in the escape from a pursuing enemy. The tail 

 becomes for the moment a more lively and interesting object than the lizard itself, and is 

 likely to distract the attention of an enemy. It is probable that the phenomena are not to 

 be explained merely by the temporary maintenance of vitality in the tissues of an amputated 

 part, but that the special activity manifested is due to accumulation through natural selection. 

 See Proc. Best. Soc. Nat. Hist. vol. xxvi. 1895, p. 388.— E. B. P.] 



[The persistence of movements in the tail under the special conditions described above 

 was doubtless mainly due, as suggested in the discussion by the President, Professor Herdman, 

 to the fact that the amputated part had lost its connection with the respiratory and circu- 

 latorv organs, by means of which the chloroform is conveyed to the tissues. — E. B. P., 

 July" 12, 1907.]" 



[Professor Herdman's explanation is doubtless the correct one, and tallies with the fact 

 that active insects, such as Humble-bees, succumb much more rapidly to volatile poisons 

 than more sluggish Beetles of the same size. At the time, however, I connected the greater 

 activity of the tail with the absence of a brain.— G. B. L., July 17, 1907.] 



