THE BUTTERFLY: STRUCTURE OF THE HEAD. 37 



occupies an exactly corresponding position behind, is also tumid hut gen- 

 erally enjoys considerable variety of contour within its own boundaries, the 

 upper portion being not infrerpiently ridged, and the sides producing little 

 proniinences. The Hanks have a regular surface, occupy most of the rear 

 of tlie head, are bounded interiorly by the occijjut and anteriorly and ex- 

 teriorly abut upcm the eyes, forming a part of the glol)e w])ich tliey 

 occupy. 



The other parts in the structure of the head wliicli require consideration 

 arc the eyes, the antennae and the mouth appendages. 



The position of the eyes has already been stated. Anteriorly they al- 

 ways have a similar boundary, l)ut posteriorly they do not occupy nearly 

 the wliolc, and sometimes scarcely more than half of the swollen mass of 

 which they form a part ; they vary too in the tumidity of the mass, in most 

 si)ecies being quite prominent, while in others and especially in the Lycae- 

 ninae they do not rise above the general contour of the surface of the 

 head ; ordinarily and in the two lower families always they are naked ; but 

 in the Lycaenidae they frequently have a portion at least of the surface 

 sparsely covered with short exceedingly delicate hairs ; and in the Xym- 

 phalidae they are often supplied with a pretty dense mass of rather long 

 hairs, always standing erect and separate, and originating at the angles of 

 the facets. The purpose of this clothing is difficult to understand. The 

 eyes (86:20,21) are composed externally of exceedingly minute hexagonal 

 facets, varying, so far as I have examined them, from about fifteen hun- 

 dred to four thousand in a square millimetre. Xo buttei-flies are provided 

 with ocelli, with the single known exception of the genus Lerema, where 

 some of the species have a single ocellus in the middle of the front in one 

 or both sexes ; while in some of the lower families of Lepidoptera the 

 nt)rmally posterior pair of ocelli alone occurs and is situated behind the 

 antennae. 



The antennae take their rise in little pits, allowing them full freedom of 

 motion between the eyes, in the line between the occiput and the front. 

 In the Lycaenidae they infringe a little upon the eyes, but in all the other 

 families they are quite free from them. They are usually not for from 

 the length of the abdomen, and are composed of a large and variable 

 number of joints ; there is occasionally a diiference of one or two joints 

 between the sexes, in favor sometimes of one, sometimes of the other. 

 They are composed of three parts : the base, the stalk and the club. The 

 base consists of two joints (the basal always smooth and naked) which are 

 different in character from the remainder, being very large and stout, and 

 capable of a great deal of motion upon one another and within the socket, 

 while the other joints have little motion upon one another. The stalk is 

 of very nearly unifonn size throughout, the joints usually very much 

 shorter near the base than in the part beyond, where they are uniform : 



