164 THE PHYSIOLOGY OF INSECT SENSES 



It is 60-70 [I long and about 1 -5 [x in diameter (Mused). A longitudinal 

 section of a rhabdomere reveals that it consists of closely packed 

 parallel tubules aligned at right angles to the long axis of the cell 

 (Fig. 84). Each is about 400 A. in diameter and 1,000-15,000 A. long. 

 The most reasonable interpretation of these tubules is that they are 

 microvilli, that is, finger-like evaginations of the retinal cell; conse- 

 quently, their boundaries are part of the cell membrane and their 

 contents are extensions of the cytoplasm (Miller, 1957; Goldsmith and 

 Philpott, 1957; Fernandez-Moran, 1958; Slifer, 1961). A fine parti- 

 culate component appears in the microvilli in fixed material. Except 

 for the small one, the rhabdomeres appear to occur as pairs, one 



Fig. 84. A. Distal tip of retinal cell 

 from the compound eye of 

 Musca domestica as recon- 

 structed by Slifer (1961) from 

 electron-micrographs of Fer- 

 nandez-Moran (1958). B. 

 Cross-section of cell with rhab- 

 domer at right. C. Section 

 through that part of rhabdomer 

 containing microvilli. (Re- 

 drawn from Slifer, 1961.) 



member of which lies opposite its twin on the far side of the ommati- 

 dium. The longitudinal axes of the microvilli in both members of a 

 pair are parallel but in a different plane from those of other pairs. The 

 core separating the rhabdomeres is a loose network of fine filaments 

 in fixed materials. In the eye of the grasshoppers Dissosteira and 

 Schistocerca the fine filaments in the matrix are closely packed and run 

 lengthwise in orderly courses. Distally this core disappears as the 

 rhabdomeres come together just below the crystalline cone. Here the 

 microvillar structure is replaced by an electron-dense structure. In the 

 eye of the dragonfly Anax Junius and in the superposition eye of the 

 moth Erebus odora there is no central matrix, since the rhabdomeres 

 meet axially. The rhabdom of the skipper consists of eight fused 

 rhabdomeres. Most workers believe that the visual pigment is located 



