G64 RADIATION BIOLOGY 



various decapod crustaceans and by Beck (1899) with the cephalopod 

 Eledone. Using similar methods, Piper (1904, 1911) obtained a spectral- 

 sensitivity curve for the latter animal. Von Bruecke and Garten (1907) 

 studied retinal action potentials in the crab Cancer. Hartline followed 

 on an assortment of arthropods (1928), including the xiphosuran Limulus, 

 and on the scallop Pecten (1938). More recently a single-ommatidium- 

 single-nerve-fiber technic has been used with Limulus (Hartline and 

 Graham, 1932a,b; Hartline, 1934, 1935, 1948; Riggs and Graham, 1940; 

 Riggs, 1940; Hartline et at., 1952). The advantages of the Limulus com- 

 pound eye in such studies were pointed out by Graham (1932) : the nerve 

 fibers from sensory units (ommatidia) extend far enough from the eye 

 before synaptic networks intervene so that electrodes can be applied to 

 isolated single fibers. Various insects have been investigated using Hart- 

 line's technic (1928) or variations of it. From such studies have come 

 many details concerning the relations between intensity and latency; 

 spectral sensitivity; duration of stimulus and intensity reciprocity rela- 

 tions; effects of area of sense organ illuminated, of temperature, of dark 

 adaptations, of diurnal rhythms, of recovery from brief illumination at 

 high intensity; variations at threshold; and the like. 



Latency has been evaluated in various invertebrates by observing 

 kinetic responses of the whole animal: in Gonionemus, the crustacean 

 Cyclops, the clams Alya and Pholas, the beetle PopiUia, and the tunicate 

 Ciona. Dark adaptation and light adapt'ation have been followed care- 

 fully in the protozoans Volvox and Peranema, the clam Mya, the slug 

 Agriolimax, and various cephalopods through evaluation of iris move- 

 ments or of pigment changes in retinal cells. Most precise measure- 

 ments of dark adaptation are those with single sensory units of the 

 Limulus eye by Harthne (1930) and Hartline and McDonald (1941, 1947). 



Dark adaptation in crustaceans has been studied by measurements of 

 rates of antennal beat in Leptodora, change in swimming direction in 

 Artemia, and modifications of the shadow reaction in the barnacle 

 Balanus. Inferences regarding dark adaptation have been obtained from 

 electrical recordings of amplified action potentials from the eyes of the 

 grasshopper Melanoplus and various moths. Modification of behavior, 

 chiefly circus movements, has afforded clues to the same process in the 

 drone fly Eristalis (Eristalomyia) and the large whirligig beetle Dineutes. 

 Changes in response to flickering light gave information on dark adap- 

 tation in the honeybee Apis (Wolf and Zerrahn-WoK, 1935), and alter- 

 ations in shadow reaction allowed similar evaluation of the tunicate Ciona 

 (Hecht, 1918b). A partial summary and chemical model for the process 

 were furnished in a paper by Hecht in 1927, but the degree to which all 

 of his analysis can be applied to sensory mechanisms alone (neglecting 

 the nervous connections and effector system) remains to be demonstrated. 



The question of spectral sensitivity in invertebrates has been studied 



