EVIDENCES— EXISTING ORGANISMS 



111 



The Significance of Homologies and Analogies. Those who 

 find special creation an adequate explanation of diverse living 

 things see nothing more in these 

 facts than the will of the Creator 

 to produce such organisms as now 

 exist. The activating force, in 

 other words, is regarded as inde- 

 pendent of the necessary materials, 

 a belief which is not liorne out 

 by observed facts. If this were 

 the foundation of life, there is every 

 reason to suppose that every crea- 

 ture would be given the best possi- 

 ble equipment for its mode of life. 

 Instead, organisms often have 

 structures which show definite 

 resemblance to those of other 

 species living under very different 

 conditions. They cannot logically 

 be supposed to have been made 

 from unspecialized raw materials. 



Fins and Flippers. Such homol- 

 ogies, very common among living 

 things, do not indicate that the 

 same end cannot be met by 

 different organs, for analogous 

 structures are also fairly common. 

 The whale has flippers which show 

 definite homology with the fore 

 limbs of terrestrial vertebrates, 

 although they are more like the 

 fins of fishes in function. Its res- 

 piration is carried on by the same 

 organs as those used by terrestrial 

 species. It would obviously be 

 better fitted for purely aquatic 



life if it could breathe without rising to the surface, but this it 

 is unable to do. On the other hand its need for such an organ as 

 the tail of the fish is met by a very similar structure which is 

 merely analogous. 



Fig. 63. — An ommatidium of Ma- 

 chilis, c, cornea; hy, corneal hy- 

 podermis; cc, crystalline cone 

 cells; i, iris pigment cells; r, re- 

 tinula; rh, rhabdom; b, basement 

 membrane; n, nerve; ap, acces- 

 sory pigment cell. (From Com- 

 stock's Introduction to Entomology, 

 with the permission of the Com- 

 stock Publishing Company.) 



