G54 RADIATION BIOLOGY 



related to dependence upon light production by mates or prey for finding 

 these important neighbors in the darkness of the depths (Chun, 1903). 

 Beddard (1884), while reporting on the isopod crustaceans collected by 

 the Challenger expedition, believed that there was a close relationship 

 between depth and the degree of degeneration of the compound eyes, 

 but unknown features of the abyssal natural history of each species make 

 generalizations highly unsatisfactory. 



Regeneration following injury to the compound eyes seems possible in 

 decapod crustaceans, although the regenerated part is not an eye but an 

 antenna-like organ. Regeneration of ommatidia appears to have ended 

 with the trilobites. Using as a criterion the failure of ommatidial areas 

 surrounded by scar tissue to line up in facet pattern with the rest of the 

 eye, Isberg (1917) concluded that formation of new ommatidia was 

 possible in this extinct class. 



Often a relatively flattened compound eye conceals externally the 

 extent of its visual field. Marginal ommatidia may be aligned with 

 their optic axes almost tangential to the surface of the body. Only 

 ideally is the external surface hemispherical and the ommatidial axis 

 ahgned in a truly radial direction. As a result, it is usual for the omma- 

 tidial axis to meet the corneal surface obliquely. To put it another way, 

 it is unusual for the ommatidial lens to lie at right angles to the omma- 

 tidial axis. As a result of this, the proportion of incident light that 

 enters the ommatidial dioptric system depends upon the plane of polari- 

 zation of the light. Sky light is characteristically polarized with refer- 

 ence to the position of the sun, and in xiphosurans and insects, at least, 

 the compound eye acting as a whole can furnish special information to 

 the central nervous system, giving the animal a sky compass. 



Von Frisch, who reported the polarization-detection feature of honey- 

 bee eyes (1949, 1950a,b), credited the discovery to Antrum, although 

 the latter did not publish an account of it until 1950. Griffin (1950) 

 and others have supported the conclusion from independent experiment, 

 and Waterman (1950, 1951) has found its counterpart among ommatidia 

 of the compound eye of the xiphosuran Limulus. In describing the 

 hymenopteran sky compass, von Frisch made use of an octagon formed 

 from pieces of Polaroid film cut in a symmetrical pattern of triangles. 

 Held toward the sky, the two triangles on some one diagonal were darkest, 

 and those on the diagonal at right angles transmitted most light; between 

 them were intergrades in transmission. It was only natural that simi- 

 larity should be suspected between the eight radially arranged pieces of 

 Polaroid film and the ring of receptor cells in an ommatidium. Perhaps 

 each ommatidium served as a separate analyzer for polarized light, and 

 the different receptor cells sent nerve impulses in a pattern advising the 

 central nervous system of unlike intensities received via the rhabdom. 

 Wolsky (1929), who investigated the corneal lenses of land isopod crusta- 



