186 MISCELLANEOUS OBJECTIONS TO THE [CHAP. VIL 



together with inheritance will have aided in an important manner 

 in their co-ordination. With the many insects which imitate 

 various objects, there is no improbability in the belief that an 

 accidental resemblance to some common object was in each case 

 the foundation for the work of natural selection, since perfected 

 through the occasional preservation of slight variations which 

 made the resemblance at all closer; and this will have been 

 carried on as long as the insect continued to vary, and as long as 

 a more and more perfect resemblance led to its escape from sharp- 

 sighted enemies. In certain species of whales there is a tendency 

 to the formation of irregular little points of horn on the palate ; 

 and it seems to be quite within the scope of natural selection to 

 preserve all favourable variations, until the points were converted 

 first into lamellated knobs or teeth, like those on the beak of a 

 goose, then into short lamellae, like those of the domestic ducks, 

 and then into lamellae, as perfect as those of the shoveller-duck, 

 and finally into the gigantic plates of baleen, as in the mouth 

 of the Greenland whale. In the family of the ducks, the lamellae 

 are first used as teeth, then partly as teeth and partly as a sifting 

 apparatus, and at last almost exclusively for this latter purpose. 



With such structures as the above lamellae of horn or whalebone, 

 habit or use can have done little or nothing, as far as we can 

 judge, towards their development. On the other hand, the trans- 

 portal of the lower eye of a flat-fish to the upper side of the head, 

 and the formation of a prehensile tail, may be attributed almost 

 wholly to continued use, together with inheritance. With respect 

 to the mammae of the higher animals, the most probable conjecture 

 is that primordially the cutaneous glands over the whole surface 

 of a marsupial sack secreted a nutritious fluid; and that these 

 glands were improved in function through natural selection, and 

 concentrated into a confined area, in which case they would have 

 formed a mamma. There is no more difficulty in understanding 

 how the branched spines of some ancient Echinoderm, which 

 served as a defence, became developed through natural selection 

 into tridactyle pedicellariae, than in understanding the develop- 

 ment of the pincers of crustaceans, through slight, serviceable 

 modifications in the ultimate and penultimate segments of a limb, 

 which was at first used solely for locomotion. In the avicularia 

 and vibracula of the Polyzoa we have organs widely different in 

 appearance developed from the same source; and with the 

 vibracula we can understand how the successive gradations might 

 have been of service. With the pollinia of orchids, the threads 

 which originally served to tie together the pollen-grains, can be 

 traced cohering into caudicles; and the steps can likewise be 

 followed by which viscid matter, such as that secreted by the 

 stigmas of ordinary flowers, and still subserving nearly but not 



