MYRIAPODA 



399 



Below the base of the cells that are to form the retinal and the nerve- 

 fiber cells (Fig. 355, rt) flattened cells {en. c) appear from which the 

 envelope cells will arise. The delicate radiating plasma processes {rhd) 

 of the retinal cells develop into the visual rods. The cells that are 

 mingled with the plasma-process bearing retinal cells now draw down in 

 contact with the eye-envelope cells and become fusiform nerve fibers. 

 Thus the undifferentiated cells marked "ri" in Fig. 355 differentiate 

 into retinal and nerve-fiber cells. The optic nerve appears to originate 

 from a prominence (op. n) at the proximal end of the eye anlage, the nerve 

 therefore growing inward to meet the optic lobe rather than growing 

 outward from it. The optic lobe and the eye recede from each other, 



Fig. 355. — Scolopendra cingulata. Section through anlage of eye. {hi) Blood cell. 

 (6sm) Basement membrane, {cut) Cuticula. {ect) Ectoderm, (en. c) Envelope cell. 

 {gglc) Ganglion cell. {It) Lentigene cell. {op. n) Proximal end of optic nerve, {pr. gglc) 

 Proliferation center of optic ganglion, {rhd) Rhabdome. {rt) Retinal cell. {Adapted from 

 Heymons.) 



but the connection between them remains. When the embryo enters 

 the so-called "fetal stage," having shed the chorion and thrown off the 

 embryonic cuticula, the first pigment granules may be seen. Soon the 

 corneagene (lentigene) cells, which surround the periphery of the eye (It) , 

 grow over the eye surface and proceed to secrete a delicate cuticula, 

 which is continuous with that of the adjacent body wall. The sub- 

 sequent development of the eye is postembryonic and may be briefly 

 described as follows: Fig. 356 represents the eye of an adult centipede. 

 Before a molt takes place, the corneagene cells (It), which normally form 

 iris-like under the cornea, close up the "pupil" by cell division and then 

 secrete a new cuticular lens, after which the central cells apparently 

 degenerate to be developed again by the peripheral corneagene cells just 

 preceding another molt. By this process the cornea is constructed. The 

 retinal cells consist of an elongate cone-like inwardly directed part 

 (visual rod) and a nucleated outwardly directed part. The A'isual rod 



