322 



GENERAL BIOLOGY 



Fig. 208. Ommatidium and Central Nervous 

 System. 



A. An ommatidium or eye-element from 

 the eye of the Lobster (after G. H. Parker). 

 c, cornea (cuticle) ; c.h., corneal hypodermis, 

 which secretes the cuticle ; co., cone cells ; cr., 

 crystalline cone ; n, nuclei ; ./., nerve fibres ; 

 r.d., distal or outer retinula cells ; r.p., prox- 

 imal or inner retinula cells ; rh., rhabdome. 



B 



B. A semi-diagrammatic view of central 

 nervous system of a crayfish, ob.l, ab.6, The 

 first and sixth abdominal ganglia ; cer., cere- 

 bral ganglion ; c.ces., circumoesophageal com- 

 missure ; I.e., longitudinal commissures of 

 ventral cord ; n.ab.L, nerves to abdominal 

 limbs; n.at.l, nerve to antennule ; n.at.2, 

 nerve to antenna ; n.ch., nerve to cheliped ; 

 n.m., nerves to limbs adjoining the mouth ; 

 o.n., optic nerve; s.ces., suboesophageal 

 ganglion; st.a., sternal artery; th.l, th.6, first 

 and sixth thoracic ganglia ; v.n., nerve to 

 proventriculus ; v.n'., nerve to hind-gut. 

 (After Borradaile.) 



Thus, three adjoining facets might view the word "Biology" in this way: 



Bio olo ogT- 



That is, facet one, would see the first three letters, facet two the 

 middle three, and facet three the last three. But since the range of each 

 facet overlaps that of the adjoining, the image formed is actually this : 



Bio ogy 



olo 



In other words, instead of an apposition image or mosaic, a super- 

 position image or continuous picture is formed.* 



*Microphotographic 

 correct one. 



tudies have definitely demonstrated that the account here given is the 



