96 GENERAL EVOLUTION. 



is exhibited between the orders Diptera and Ilymenoptera among 

 insects. None of these comparisons can be allowed, of course, 

 without the most searching anatomical and embryological analysis. 



This heterology is what Swaiuson and others called "analogy" 

 as distinguished from affinity. It gene7'ally relates genera of dif- 

 ferent zoological regions. Mimetic analogy, on the contrary, re- 

 lates genera of the same region ; it is a superficial imitation which 

 has occurred to critical biologists, and is of much interest, though 

 as yet but little investigated. It has as yet been observed in ex- 

 ternal characters only, but occurs in internal also ; it has been 

 accounted for in the first case by the supposed immunity from 

 enemies arising from resemblance to well-defended types. No 

 such explanation will, however, answer in the latter case. I be- 

 lieve such coincidences express merely the developmental type 

 common to many heterologous series of a given zoological "re- 

 gion " ; this will be alluded to a few pages later. 



We naturally inquire. Is there anything in the food, the vege- 

 tation, or the temperature to account for this apparent diversity 

 in the different regions ? Are there not carnivora, herbivora, 

 seed-eaters, insectivores, and tree-climbers, where game and grass, 

 seeds and insects and forests grow the world over ? We answer 

 undoubtedly there are, and these adaptations to food and climate 

 are indeed as nothing in the general plan of creation, for every 

 type of every age has performed these functions successively. 



3. Of Heterology.'^ 



This relation will be exhibited by a few examples from groups 



known to the writer, commencing with the Batrachia anura. 



Raniformes. Arcifeki. 



External metatarsal free. 



Aquatic. Rana. Pseudis. 



Metatars. shovel. Hoplobatrachus. Mixophyes. 



External metatarsal attached. 



Feet webbed. 

 Metatars. shovel. Pyxiccphalus. Tomopterna. 



* Some of the cases below cited as heterology I believe to be truly of this char- 

 acter ; but some others are probably not such, but are merely series of genera pre- 

 senting similar structural peculiarities as consequences of the operation of identical 

 laws. I would place under this head, and withdraw from the homologous class, the 

 families of Lacertilia Leptoglossa, Diploglossa, and Typhlophthcdmi, those of the Old 

 and New World Quadntmana and those of Cephalopoda. These distinct modes of 

 origin of corresponding forms have been recently termed, by Lancaster, homogeny 

 in the case of homologous groups, and homoplassy when the imitative types are on 

 distinct lines. (Ed. 1886.) 



