OCTOBEE 3, 1913] 



SCIENCE 



461 



Bulla auris of PUoplatecarpus (Fytlionomorphe) 



and certain whales; if tympanic ^ quadrate. 

 Grasping instruments or nippers in Arthropods: 



pedipalps of Fliryne; chelee of squill; first 



pair of mantis 's legs. 

 General appearance of moles and Notoryctes, if 



both considered as mammals; of gulls and 



petrels, if considered as birds. 

 EomoBOtely : 



Heterodactyle foot of trogons (3-4/2.1). 

 Jumping foot of Macropus, Dipus, Tarsius. 

 Intertarsal and cruro-tarsal joint. 

 Fusion and elongation of the three middle 



metatarsals of Dipus and BJiea. 

 Paddles of ichthyosaurs. Turtles, whales, pen- 

 guins. 

 "Wings" of pterosaurs and bats. 

 Long flexible bill of Apieryx and snipes. 

 Proteroglyph dentition of cobras and soleno- 



glyph dentition of vipers. 

 Loss of the shell of Limax and Aplysia. 

 Complex molar pattern of horse and cow. 

 Parately : 



Bivalve shell of brachiopods and lamellibranchs. 



Stretcher-sesamoid bone of pterodactyls (radial 



carpal) ; of flying squirrels (on pisiform) ; of 



Anomalurus (on olecranon). 

 Bulla auris of pythonomorph (quadrate) and 



whale (tympanic) ; is incus = quadrate. 

 "Wings" of pterosaurs, or bats, and birds. 



The distinction between these three cate- 

 gories must be vague because that between 

 homology and analogj^ is also arbitrary, 

 depending upon the standpoint of compari- 

 son. As lateral outgrowths of vertebrse all 

 ribs are homogenes, but if there are at least 

 hsemal and pleural ribs then those organs 

 are not homologous even within the class 

 of fishes. If we trace a common origin far 

 enough back we arrive near bedrock with 

 the germinal layers. So there are specific, 

 generic, ordinal, etc., homoplasies. The po- 

 tentiality of resemblance increases with the 

 kinship of the material. 



Bateson, in his study of homoeosis, has 

 rightly made the solemn quotation : ' ' There 

 is the flesh of fishes . . . birds . . . beasts, 

 etc. ' ' Their fiesh will not and can not react 



in exactly the same way under otherwise 

 precisely the same conditions, since each 

 kind of flesh is already biased, encumbered 

 by inheritances. If a certain resemblance 

 between a reptile and mammal dates from 

 Permian times, it may be homogenous, like 

 the pentadactyle limb which as such has 

 persisted; but if that resemblance has first 

 appeared in the Cretaceous period it is 

 homoplastic, because it was brought about 

 long after the class division. To eases 

 within the same order we give the benefit 

 of the doubt more readily than if the re- 

 semblance concerned members of two or- 

 ders, and between the phyla we rightly 

 seek no connection. However, so strongly 

 is our mode of thinking influenced by the 

 principle of descent that, if the same fea- 

 ture happen to crop up in more than two 

 orders, we are biased against homoplasy. 



The readiness with which certain homo- 

 plasies appear in related groups seems to 

 be responsible for the confounding of the 

 potentiality of convergent adaptation with 

 a latent disposition, as if such cases of 

 homoplasy were a kind of temporarily de- 

 ferred repetition, i. e., after all due to in- 

 heritance. This view instances certain re- 

 curring tooth patterns, which, developing 

 in the embrj^onic teeth, are said not to be 

 due to active adaptation or acquisition but 

 to selection of accomplished variations, be- 

 cause it is held inconceivable that use, food, 

 etc., should act upon a flnished tooth. It is 

 not so very difficult to approach the solu- 

 tion of this apparently contradictory prob- 

 lem. Teeth, like feathers, can be influenced 

 long before they are ready by the life ex- 

 periences of their predecessors. A very 

 potent factor in the evolution of homo- 

 plasies is correlation, which is sympathy, 

 just as inheritance is reminiscence. The 

 introduction of a single new feature may 

 affect the whole organism profoundly, and 

 one serious case of isotely may arouse un- 



