392 



CHARLES H. SPURGEON. 



degenerated of these thicl^enings are in the anterio-lateral or 

 retinal portion of the optic stalk. This point is well illustrated 

 in Figs. 5 and 8 and photomicrographs B, C and E. 



The retinal region of the hypodermis has two or three distinct 

 layers of cells, while the rest of the hypodermis has only one 

 layer of cells, except in secondary thickenings such as are shown 

 in Figs. 6 and 7 and photomicrograph A . The cells of the retinal 

 hypodermis in C. setosus and C. pellucidus differ in size, shape and 

 staining properties from the other cells of the hypodermis. My 

 drawings and photomicrographs show that the hypodermis is 

 considerable thicker in the retinal region than elsewhere. Here 



I 



Fig. 8. Cell structure of the retinal region of the eye of C. setosus from a section 

 similar to those of photomicrographs B, C and E. 



again I differ from Parker who said of the hypodermis in C. 

 setosus: "At least it is not thicker in the region of the retina 

 than at many other places." 



The ommatidium or ocellus (Fig. 9) is the unit of structure of 

 the compound eyes of Arthropoda. The functional eye of 

 Cambarus has four layers of cells in the developing retinal 

 hypodermis; the corneagen, the vitrellse, the retinulae and pig- 

 ment cells. 



The diopteric structures of the eye, such as the lens, cone and 



