CONTKIBUTIONS TO THE AnATOMT OF THE MiLK-WEED BUTTEKFLY [DanaiS AvcMppuS 



Fabr.). By Edward Burgess. 



GrENERAL students of comparative anatomy wishing to gain some knowledge of the 

 structure of the Lepidoptera find their way blocked by the lack of some suitable modern 

 monograph on any species of this group to which they may turn. I have, therefore, 

 attempted to fill this gap to some extent by a preliminary sketch of the anatomy of the 

 Milk-weed Butterfly {Danais Archippus Fabr.), choosing this species as a type of the 

 order, partly on account of its large size, common occurrence and wide distribution — for 

 it is found nearly the world over — and, partly, because the anatomy of no species of 

 Danaidae has yet been studied. 



The present paper treats only of the general anatomy of the perfect insect, leaving the 

 consideration of the larval and pupal structure and development, as well as the histology, 

 to the future investigations of myself or others. 



The special student, already acquainted with the present state of our knowledge of but- 

 terfly anatomy, will find new observations on the maxillae and suctorial mechanism of 

 these insects ; on the course of the dorsal vessel ; and on the structure and mechanism of 

 the male genital armature. 



I. StKUCTUEE of the ExOSKELETOlSr. 



Head. (See pi. 1, figs. 1 and 3.) The roof of the head is formed by the epicranium, 

 which bears on its sides the large eyes, and, in front, the antennae. The posterior aspect 

 of the epicranium is called the occiput, while the front is the region immediately above 

 and between the antennae. The small triangular areas, on either side, and below the face 

 are the cheeks or genae {g.). The face includes the region below the antennae, and is 

 formed chiefly by the large, vaulted clypeus (c), whose arc-shaped lateral boundaries are 

 well-marked, while above it passes directly into the epicranium, without any suture or line 

 of demarcation as found in many insects. The compound eyes (oc.) are very large and 

 protruding ; the ring-like ridges on which they are borne are termed the orbits (or.). Sim- 

 ple eyes, or ocelli, are not found in the butterflies, although there are two in moths. 



The antennae articulate with the epicranium by a " ball and socket " joint ; the ball 

 being formed by the large first and smaller second antennal joints (see fig. 3), is deeply 

 inserted in the antennal fossa or socket. The succeeding joints are cylindrical, and of 

 much less diameter than the ball; they are about forty-five in number, and of nearly uni- 

 form size till towards the tip, where the last ten gradually expand, becoming also shorter, 

 and form the "^club," which characterizes the antennae of the diurnal Lepidoptera. 



