no MO PT ERA 



443 



Fig. 515. — A depigmented "acces- 

 sory eye" of Psetidococcus de- 

 structor: c, cornea; h, corneal 

 hypodermis ; i, iris cell; r, reti- 

 nal cells; n, nerve. 



The structure and development of the eyes of the male of the common mealy- 

 bug, Pseudococciis (Dactylopms) destructor, was studied by Krecker ('09). In 

 this insect there is on each side of the head a very small eye; since these are the 

 only eyes possessed by the young nymphs, they were termed by Krecker the 

 primary eyes. In the adult, in addition to the primary eyes, there are two pairs of 

 eyes, one pair on the dorsal aspect of the head, and a second pair on the ventral 

 aspect; these he termed the accessory eyes. 



The so-called primary eyes are very de- 

 generate, in the adult at least. There is a 

 lens below which there are a few retinal cells; 

 but there is no corneal hypodermis, no rhab- 

 doms, and no iris. 



The development of the so-called acces- 

 sory eyes is greatly retarded. The histo- 

 blasts from which they are developed appear 

 in the latter part of the second nymphal 

 stadium or in the beginning of the third; 

 these are thickenings of the hypodermis. 

 When fully developed as seen in the adult, 

 the accessory eyes (Fig. 515) have a large 

 circular cornea, followed by a comparatively 

 thin layer of corneal hypodermis, encircling 

 which is a single row of large iris cells. Below 

 the corneal hypodermis there is a crescent- 

 shaped area of polygonal rods (rhabdoms), 

 which are terminally situated upon the ret- 

 inal cells. From the proximal end of the 

 retinal cells extend the nerve fibrils which 

 join to form the optic nerve, which follows 



the contour of the head to enter the bram lateral- 

 ly. Reddish brown pigment fills the retina, the iris, 

 and also a ridge surrounding the eyes. There are 

 no cells which function as pigment cells alone. 



The antennas of the males are lon^ and 

 slender, and consist of from six to thirteen 

 segments; in some of the Margarodinag they 

 are branched or fiabellate. The antennce of 

 adult females exhibit great variations in 

 structure; they may be well developed and 

 consist of as many as eleven segments; or 

 they may be greatly reduced in size and in 

 the number of segments; in some species 

 they are either vestigial or entirely wanting 

 in adult females. 



The mouth-parts are situated on the 



hind part of the ventral aspect of the head, 



and often extend caudad of the first pair of 



legs. In front of the beak there is a densely 



chitinized area, which includes the clypeus, 



Fig. 516.— Mouth-parts of a ^^gjabj^jj^ and themandibularandmaxillary 



cWtwied'Jfin ftrS^elerites. In cleared specimens there can be 



the beak; B, the beak; /, seen withm this area a complicated endo- 



labrum; 0, oesophagus; skeleton (Fig. 516, A). 



s, loop of mandibular and 'pj^g labium (Fig. 516, B), which is com- 

 maxillary sete^Jn ^the^^^^^ termed the beak or rostrum, ^consists 



crumena 

 lese.) 



of three segments in a few forms found in 



