EXTERNAL ANATOMY 29 



The labrum so far as observed is always obsolete. The cephalic 

 portion of the ventral aspect of the head bears the eyes and the 

 antennae and the caudal portion the mouth-parts. The latter are 

 attached between the first pair of legs and usually in line with the 

 first pair of spiracles. 



Eyes. The eyes, when present in the female, are always 

 simple. They are comparatively large in the active species and 

 sometimes, as in Orthezia, are placed on short projections. The 

 portion representing the eye can usually be recognized even in 

 treated specimens from the presence of pigment. The eyes of the 

 female are sometimes designated as the primary eyes, because they 

 persist through out all the nymphal stages and are present in the 

 adult. The eyes of the male are compound in the Monophlebinae, 

 the Xylococcinae, the Margarodinae, and the Ortheziinae. The 

 external part of each separate compound eye, a facet, is strongly 

 convex so that the compound eye appears as a whole coarsely 

 granular. In the subfamilies with compound eyes certain species 

 are also provided with two simple eyes or true ocelli, which are 

 sometimes located between the compound eyes but more often 

 adjacent to their caudal margin. In the other subfamilies the 

 compound eyes are represented by groups of simple eyes which 

 are arranged in a semicircle on each side of the head. The number 

 of simple eyes varies greatly in the different genera. They are 

 most numerous in the Phenacoleachiinae, eight on each side, 

 where they form almost a complete circle, but the usual number is 

 from three to five on each side. There is usually a pair of large 

 facets on the dorsal and another on the ventral aspect. It has 

 been claimed by some that the ventral pair of facets is developed 

 from the mouth-parts which are always stated to be wanting. In the 

 wingless males the eyes are limited to two facets, one on each side 

 of the head as in the female, but there is no reason other than 

 similarity in position for considering them homologous with the 

 primary eyes of the female. 



Each of the simple eyes of the nymphal and adult female and 

 of the first nymphal male and of the adult male with simple eyes 

 is known as an ocellana. This term is applied to all the simple 

 eyes, other than ocelli, of all Exometabola. In order to distinguish 

 the simple eyes other than ocelli of other insects, those found in 

 nymphal and adult Apterygota are known as ocellalae and those of 

 the larvae of Entometabola as ocellarae. The position of one pair 

 of ocellanae on the dorsal aspect of the head of certain males, 

 which are not in line with the other ocellanae, would suggest that 



