REVIEWS. 421 
the bodies of these animals, and while in most of the radiates it is 
difficult to detect any line dividing their body into halves, the 
insects, and indeed all the articulates, are as a rule symmetrical, 
one-half of the body, together with its appendages, exactly repeat- 
ing the opposite. As our authors remark, however, some of the 
Crustacea are asymmetrically developed, and they give as exam- 
ples, the entire body of Bopyrus and Peltogaster, low parasitic 
forms, and the claws of many Decapods, such as the lobster and 
many species of shrimps. They further remark :— 
“We are not aware that any cases of asymmetry have been 
recorded among the worms ; and certainly very few among insects ; 
there are occasionally slight differences in the right and “left man- 
dibles of some mandibulates [such as beetles], and Coccus has 
culidz is unsymmetrical. 
A figure of this organ, belonging to a species of fly, Phora, is 
given in illustration, with the left clasp very much stouter and 
somewhat longer than the right one. 
In studying the external genital organs of the males of Nisoni- 
ades, a genus of butterflies belonging to the skippers, a most 
remarkable asymmetry was detected between the opposite clasps 
of the same individual. This is found more or less marked in all 
the species yet known, the left clasp ‘‘ with some minor excep- 
tions,” being always more highly developed than the right. 
It is difficult to account for this asymmetry. The males are 
much more numerous than the other sex, and the authors are in- 
clined to think that ‘‘the excessive development of these parts in 
the male, is in correlation with their superior numbers, ensuring 
beyond doubt, the impregnation of every female; we do not, how- 
ever, see how asymmetry gives any superior advantage.” A de- 
scription of these parts in the different species follows, and eleven 
new species are described. It is a pity that other than these 
secondary sexual characters were not added for the better discrim- 
ination of the species of so large and difficult a genus — but fur- 
ther descriptions of the new forms are probably reserved for 
another occasion. 
