386 



HITCHCOCK'S ANATOMY 



that of the lowest invertebrata, being nothing but two pig- 

 mentary spots. The eye is but slightly movable in fishes, 

 since the body, and consequently the head, can be so readily 

 moved in any direction through the water. 



Fig. 3 54, 709. Compound Eyes 



— Number of F a c e t s . — 

 The eyes of many of the 

 articulate animals are con- 

 structed upon the com- 

 pound type, that is, the 

 visual organs are made up 

 of an aggregation of single 

 eyes placed upon each side 

 of the head, each one of 

 which is a complete visual 

 instrument, but can re- 

 ceive and bring to a focus 

 only those rays of light 

 which come to it from a particular direction. In many in- 

 sects each composite eye forms a hemispherical protuber- 

 ance upon the side of the head, which, when examined by the 



Fig. 355. 



A 



Head and Compound Eyes of the Bee, show- 

 J*\g the Ocelli in situ on one side (A), and dis- 

 placed on the other (B). a, a, a, Stemraata. 

 b, Antennas. 



A, Section of the Eye of Melolontha Vulgaris (Cockchaffer). B, A portion more highly 

 Magnified, a, Facets of the Cornea, b, Transparent Pyramids surrounded with Pig- 

 ment, c, Fibers of the Optic Nerve, d, Trunk of the Optic Nerve. 



What are the pigmentary spots? 709. What are compound eyes? What sub-kingdom 

 do they characterize ? How does the eye appear on many insects ? 



