No. 585] 



A STUDY OF ASYMMETRY 



f>23 



netic oddities; the hornbill Rhinoplax, with an asymmet- 

 rical tail, further peculiar in having a solid casque, an 

 elongate central rectrix, and a naked patch on the back 

 extending to the sides of the head, is found in the warm 

 Malayan region; the crossbills (Loxia), with the tips of 

 the mandibles crossed and a corresponding distortion in 

 the bones of the head are all subarctic or cold temperate 

 forms; and the owls with one ear greatly larger than the 

 other, so far as has been determined are, like the cross- 

 bills, birds of the colder regions; and that among the 

 fishes and similar types the very asymmetrical Anableps 

 lives in the warm tropical littoral, while the flatfishes 

 (PleuronectidaB) are chiefly developed in the warm trop- 

 ical littoral, and in cold and shallow water, and the asym- 

 metrical forms of " Amphioxus" (using the term in its 

 broadest sense) occur in warm and shallow water. 



Further it is interesting to recall that animals under 

 domestication — that is, living under conditions which 

 typically lead to a more or less degenerate diversity in 

 form and color — commonly develop asymmetry of action 

 which, though usually occurring in the form of individual 

 variation, may become very marked as in the case of the 

 Japanese waltzing mice, as well as pronounced, though 

 irregular and sporadic, asymmetry in color pattern, denti- 

 tion, and other features. 



More or less pronounced asymmetry undoubtedly exists 

 in many types in which up to now it has been overlooked, 

 and the conclusions reached in the present paper may be 

 modified somewhat when a better knowledge of the sub- 

 ject is attained; but on the other hand it is scarcely prob- 

 able that many instances of marked asymmetry have es- 

 caped the notice of naturalists. 



The Different Types of Crixoidal Asymmetry 

 In the great majority of the recent crinoids the body is 

 almost perfectly pentamerous, being composed of five 

 similar sectors. The presence of a small muscular cone 

 in the posterior interradius, at the summit of which is 



