206 DARWINISM 



those feeding on particular species of plants would rapidly 

 acquire the j)eculiar tints and markings best adapted to 

 conceal them ui)on those plants. Then, every little variation 

 that, once in a hundred years perhaps, led to the preservation 

 of some larva which was thereby rather better concealed than 

 its fellows, would form the starting-point of a further 

 development, leading ultimately to that perfection of imitation 

 in details which now astonishes us. The researches of Dr. 

 Weissmann illustrate this progressive adaj)tation. The very 

 young larvse of several species are green or yelloAvish without 

 any markings ; they then, in subsequent moults, obtain certain 

 markings, some of which are often lost again before the larva 

 is fully grown. The early stages of those species which, 

 like elephant hawk -moths (Chserocampa), have the anterior 

 segments elongated and retractile, with large eye -like spots 

 to imitate the head of a vertebrate, are at first like those of 

 non-retractile species, the anterior segments being as large as 

 the rest. After the first moult they become smaller, com- 

 paratively; but it is only after the second moult that the 

 ocelli begin to appear, and these are not fully defined till after 

 the third moult. This progressive development of the in- 

 dividual — the ontogeny — gives us a clue to the ancestral 

 develojiment of the whole race — the phylogeny ; and we are 

 enabled to picture to ourselves the very slow and gradual 

 steps by which the existing perfect adaptation has been 

 brought about. In many larvae great variability still exists, 

 and in some there are two or more distinctly-coloured forms 

 —usually a dark and a light or a brown and a green form. 

 The larva of the humming-bird hawk -moth (Macroglossa 

 stellatarum) varies in this manner, and Dr. Weissmann raised 

 five varieties from a batch of eggs from one moth. It feeds 

 on species of bedstraw (Galium verum and G. mollugo), and 

 as the green forms are less abundant than the brown, it has 

 probably undergone some recent change of food -plant or 

 of habits which renders brown the more protective colour. 



Special Protective Colouring of Butterflies. 



We Avill now consider a fcAV cases of special protective 

 colouring in the perfect butterfly or moth. Mr. Mansel 

 Weale states that in South Africa there is a great prevalence 



