THE GERM-PLASM THEORY 



357 



correlated variations, and in very many cases the breeder eau* 

 a second or third character, on which ho had not fixed hia attentioo 

 to vary m addition to the one he was aiming at. Bui such con' 

 comitant variations are not necessary or inevitable in ,11 cases' and 

 indeed we need not refer them all to a true correlation of the parts 

 but may suppose that they depend not infrequently on the Paultin. 

 of our power of observation, which is not sufficiently keen to control 

 several parts of the body at 

 one time, and to notice minimal 

 variations in parts on which 

 we have not specially fixed our 

 attention. 



So much, at least, is certain, 

 that in all these cases of the 

 artificial alteration of individual 

 characters the germ-plasm is in 

 some way changed, but always 

 in such a way that it differs 

 from that of the ancestral form 

 through such variations alone, 

 and the effect of these is that 

 only the altered parts are in- 

 fluenced thereby, and not the 

 whole organism. This again is 

 but another way of saying that 

 only the determinants of these 

 parts have altered. 



We can see from a thousand 

 cases that exactly the same 

 happens in a state of nature, 

 that there, too, one part changes 

 after another, until the highest 

 possible degree of adaptation to 

 the conditions has been attained. 

 In the mimetic resemblance to 

 leaves exhibited among butterflies this is most clearly seen, For here 

 we are familiar with the model — the leaf — and we see how one species 

 approximates to it in a general way only in the total col< mr, li< »w i >thers 

 develop a brown stripe crossing the posterior wing i >1 Jiquely, » i thai. t« > 

 a certain extent, it resembles the midrib of a leaf, how in a third species 

 this stripe is continued for some distance forward across tli<' anterior 

 wing, in a fourth it goes a little further, until, finally, in a fifth, it 



i. z 



Fig. 13. Kallima paralecta, from India: 

 showing the right under Biirface in 1 1 > « - 

 resting pose. K, head. £1, palps. B. limbs. 

 V, fore wing. H, hind wing. Sf, ' tail ' of the 

 latter, representing the stalk of tin' leaf. 

 gl l and gP f transparent spots. . remains 



of ' eye-spots.' Sc7;, a 'mould '-spot. 



