218 Treubia Vol. Ill, 2. 



L. 



R 















1 



Panesthia mandarineat SAUSSURE. 

 (O. U. M. collection) 



Borneo ^ WALLACE 



Singapore HORSLEY 



Panesthia biglumis, SAUSSURE. 

 (O, U.M. collection). 



L. " R. 



Philippines coll.? (broken) 



Panesthia flavipennis, WOOD-MASON. 

 (O. U. M. collection). 



L. R. 



Naga Hills coll.? 



The above tables, comprising 92 specimens of eight different species 

 of Panesthia, show that in 60 cases the number of species on the two 

 anterior femora was equal, that in 25 cases the spines on the right femora 

 preponderated, and only in 7 those of left. 



An examination of 17 examples of a closely allied form, Salganea 

 morlo, Burmeister, partly from the Buitetizorg collection and partly from 

 the O. U. M., led, curiously enough to quite different results. Though the 

 number of spines varied here within the same limits, viz. from nil to five, 

 they were in six cases equal on the two anterior femora; in six those of 

 the right preponderated and in five those of the left. They were therefore 

 as equally distributed as possible. 



ASYMMETRY IN BLATTIDAE. 



We may take it as established that variation in the number of spines 

 in the anterior femora of Panesthia is of common occurence; that the 

 number may very even between the right and the left side of the same 

 individual, and that it is generally the left side in which the number o^ 

 spines is reduced. 



With the tegmina of Blattidae asymmetry is, of course, the rule. In by 

 far the greater number of species the two tegmina cross each other thus 

 that the left tegmen covers a portion of the right, and the covered portion 

 is then always of a less firm texture and of a different, duller colour. No 

 doubt, it is of advantage to these insects that their flat and soft body should 

 be protected by a double layer. However, in a few instances the tegmina 

 meet in a straight line, without crossing each other (Diploptera, Euthyr- 

 rapha, Aphlebia, Hypnorna), 



