The Eyes of Dactylopius. 75 



was expericiiceil in ohtaining true sectioiis. The results here given 

 are based on as accurate axial sections as could bc secured. 



To resuino tlie discussion of the eyes, in tlie 2)resent investigation 

 especial attention has been given to tlie accessory eyes of the male. 

 It has long been supposed that the mouth parts of the male disappear 

 about the time of the second molt or the third nymph stage, and that 

 in their stead develop a pair of eyes. A dorsal pair also appears at 

 the same time. Because they are not present throughout the entire 

 lifetime of the insect these four eyes are called accessory by Berelese, 

 and they will be so designated in the following description. 



The eyes as they appear in the adult will be described first, after 

 which their development will be eonsidered. 



The ventral eyes, the larger of the two pairs, are situated one on 

 each side of the median line in the caudal half of the ventral aspect 

 of the head. They appear as two large, ovoid, closely approximated 

 areas (each (JO x 50 micra). The dark central portion is surrounded 

 by an outer band of red (Fig. 1). The dorsal eyes lie just caudad of 

 the base of the antennae on the dorso-lateral line of the head. They 

 are circular and entirely black, and about 30 micra in diameter (Fig. 2). 

 The primary or lateral eyes can best be seen from the ventral side; 

 as two. black, bead-like projections with translucent tips on the lateral 

 surface of the head, opposite the cephalic half of the ventral eyes 

 (Fig. 1 and 2). 



The accessory eyes and perhaps the primary eyes as well are di- 

 plostichous, i. e. consist of two cell layers which are best seen in an 

 axial section. Their general appearance, to a great extent, resembles 

 those eyes found among spiders in which the visual rods are at the 

 distal end of the retinal cells — the so-called prebacillar eyes, examples 

 of which are found among the Drassidae. 



The dorsal eyes are similar in structure to those on the ventral 

 surface but they do not extend so far entad as do the latter, a longi- 

 tudinal section appearing like a shallow bowl (Fig. 6). A similar section 

 of the ventral eyes taken across the head is slightly triangulär with 

 apex directed entad. The base of this triangle is depressed into a 

 concavity in which rests the circular lens (Fig. 9). Immediately beneath 

 it is the comparatively thin corneal hypodermis which is followed 

 by a clear, crescent shaped space, the crystaline portion of Targioni- 

 TozzETTi and Berelese. This is composed of the visual rods. Finally, 

 there is the densely pigmented, reddish brown, proximal or retinal 

 laver. At the base of these cells is a bed of nervous tissue, most abundant 



