1 70 Mary Isabelle Steele 



The compound eye may be regarded as that part of the optic 

 apparatus contained in the eye stalk. It consists of a large num- 

 ber of ommatidia occupying the distal end of the stalk and a 

 series of four ganglia which extend through the axial portion of the 

 stalk. This series of ganglia for present purposes may be regarded 

 as a compound ganglion composed of four rather distinct sections 

 or ganglionic masses united to each other by nerve fibers. The 

 ommatidia are connected with the distal section of the optic 

 ganglion by the retinular nerve fibers. The optic nerve passes 

 inward from the proximal section of the ganglion to unite the eye 

 with the brain. The basement membrane forms a sort of partition 

 between the ommatidia and the optic ganglion. The transparent 

 chitinous covering over the ommatidial region is known as the 

 cornea. 



Each ommatidium is composed of the following cells : two cor- 

 neal hypodermal cells, four cone cells, two distal retinular cells, 

 eight proximal retinular cells one of which is rudimentary, and a 

 variable but small number of accessory pigment cells. Black 

 pigment granules are contained in both proximal and distal 

 retinulae and are found only in these cells. The yellowish pigment 

 is confined exclusively to the accessory pigment cells. The differ- 

 ent cells enumerated above give rise to the structures that consti- 

 tute a complete ommatidium. The two corneal hypodermal cells 

 secrete the square corneal facet which covers the outer surface of 

 the ommatidium. Immediately beneath the corneal hypodermal 

 cells is the crystalline cone formed by the four cone cells. The 

 nuclei of these cells are located in their distal ends. The main 

 body of the cone appears as a dense hyaline secretion. Proximally 

 the cone is less dense in structure and tapers to a slender stalk 

 lying between the cone and rhabdom. The rhabdom, according to 

 my observations, is a swollen spindle-shaped structure proximal to 

 the inner ends of the cone cells. The distal retinular cells lie near 

 the inner end of the cone; the proximal retinulae surround the 

 distal end of the rhabdom. The proximal processes of the retin- 

 ulae extend over the rhabdom and pass through the basement 

 membrane as the retinular nerve fibers to enter the optic ganglion 

 below. The accessory pigment cells lie both above and below the 

 basement membrane. 



