88 JOURNAL, R.A.S. (CEYLON). [VOL. XV. 



The hour-glass shaped mark on the backs of our frogs is 

 an interesting instance. This cannot add to their power of 

 concealment or benefit them in any way that we can see ; 

 as a fact, in Rhacophorus maculatus, Gray, it is of very rare 

 occurrence, it is specific in R. cruciger, Blyth, and R. eques, 

 Giinther. In R. micro tympanum, Giinther, we have a 

 modified form of it, described in a very different way by 

 Dr. Boulenger, but evidently merely a modification. 



The common form from which these species have been 

 derived no doubt possessed this character. The occurrence 

 of peculiar markings in many species of those groups which 

 we call genera is very common, and frequently enables us 

 at once to refer the species before us to its proper place. 



The interest of these local varieties consists in their study 

 bringing us to the beginning of things. Good work is being 

 done by many naturalists in careful observations and 

 measurements, like the Papers, for instance, by Mr. H. 

 Thompson on the common English shore crab, in the 

 Proceedings of the Royal Society, October, 1896, and my 

 principal object has been to show what advantages we possess 

 in Ceylon for following the subject up. 



Considering the millions of ancestors any living specimen 

 must have had, the wonder is that species breed so true. 

 Where the variation is very small — for I doubt if a case could 

 be proved in the whole animal kingdom where there is none 

 — it arises in a great degree from the perfection of adaptation 

 to its environment obtained by the species. We have such 

 instances in cockroaches, rats, sparrows, and other semi- 

 parasites of man, who are able to follow him in almost any 

 climate, and under almost all conditions which he is able to 

 live in himself. We see the same thing in some birds of 

 very wide geographical distribution. 



The great opposition that Darwinism received at first was 

 owing to the belief that his doctrine implied the descent of 

 man from the monkey: the real reading of course being 

 that man and the existing monkeys have branched off from 



