642 RADIATION BIOLOGY 



trically, and others (e.g., van Weel and There, 1935, 1936) investigated 

 astigmatism in relation to the slit pupil. Heidermanns (1928) concluded 

 that Seyia accommodated well for distance but that this was the mecha- 

 nism for distance estimation, since vision appeared to be monocular (with 

 only shght overlap in the fields of the two eyes). The image is clear, 

 and he beUeved it to be appreciated both in detail and in color. On the 

 basis of conditioned responses, Buytendijk (1933) concluded, however, 

 that the eyes were used more in avoiding danger than in finding food; 

 reaction times were very long even when the animal was hungry. The 

 form of the pupil, moreover, seemed governed to a large extent by emo- 

 tional state. Van Weel and Thore found pupil-control centers in the 

 optic peduncle and subesophageal ganglion but reported that, in an 

 unexcited intact animal, pupil aperture followed light-intensity changes. 

 Steinach (1901a,b), by contrast, concluded that the reflex movements to 

 light were based on a dermal sensitivity in the tentacles, not in the eyes. 

 Baglioni's experiments (1909) showed similar difficulty in blinded speci- 

 mens and led to the conclusion that vision, touch (including water move- 

 ments), and taste all acted together inseparably, so that delay in capture 

 of food when use of the eyes was prevented did not represent an accurate 

 measure of the function of the eyes alone. Chun (1903) commented 

 extensively on the value of eyes to the deep-sea cephalopods in bathic 

 levels, where light production is a characteristic ability. More direct 

 and valuable evidence has been made available from study of electrical 

 action currents from cephalopod eyes stimulated by fight: in Eledone by 

 Beck (1899) and Piper (1904, 1911) and in the squid Loligo by Therman 

 (1940). Piper (1904) obtained a good spectral-sensitivity curve. Ther- 

 man investigated the electrical aspects of dark adaptation and effects of 

 drugs. There can be no question that the eyes of cephalopods are sensi- 

 tive to light, but, as in the vertebrate, the central nervous system is so 

 highly developed that simple responses are seldom elicited when a captive 

 animal is examined as a whole. 



ARTHROPODA 



The development of obvious eyes, both simple and compound, among 

 the several classes of arthropods and the evident responses to light 

 observable among the multitudinous genera have served to draw atten- 

 tion away from a broader sensitivity of a lower order — a dermal photo- 

 sensitivity, or a photosensory activity within ganglionic areas. That 

 decapod crustaceans include such mechanisms has been pointed out by 

 Prosser (1934), Welsh (1934), and Schallek (1942) for the sixth abdomi- 

 nal ganglion of the crayfish and by Hess (1938b, 1940) for Crangon and 

 the spiny lobster Panulirus. In Crangon and Honiarus all abdominal 

 segments appeared equally sensitive to light, and on the basis of regional 

 photosensitivity of the uropods, Hess concluded that "cell bodies of the 



