INVERTEBRATE PHOTORECEPTORS 659 



Ephestia (Klingebeil, 1938) and the fly Drosophila (McEwen, 1918; Brown 

 and Hall, 1936). In the silkworm Bombyx different racial strains respond 

 differently to light stimulation, although no basis for this has been found 

 in the eyes (Waitzinger, 1933). 



ECHINODERMATA 



Langeloh (1937) has contributed the only account of light responses in 

 crinoids; in Antcdon he found the whole upper surface of the body to be 

 photosensitive. Sudden illumination produced contraction of the longi- 

 tudinal musculature, but shadowing had no apparent influence. 



Asteroidea. Haeckel (1859) and later workers (see van Weel, 1935; 

 vSmith, 1937) described the compound ocelli at the tips of the arms of 

 such starfish as Asterias, Asterina, and Asteracanthion. Wilson (1860) 

 reported movements in the whole ocellar area which changed their posi- 

 tions in Solaster. Jourdain (1865), who distinguished between idoscopic 

 (image-forming) eyes and photoscopic (responding to intensity and per- 

 haps also direction) eyes, indicated that, although starfish ocelli appear 

 capable of image formation, the relations of the parts merely provided 

 concentration of light on the sensitive cells below the lens. Hamann 

 (1883a) went farther in claiming that the ocelli were not light-sensitive 

 at all. Jennings (1907), however, reported that Asterias in righting itself 

 always turned toward the side away from lateral illumination and that, 

 if prevented from escaping from a flat surface, it turned its arm tips 

 away from the light. In a vessel with black sides it moved to the sides 

 even when this involved approaching the light source, thereb}^ suggesting 

 vision of some sort. Bohn (1908) and von Frisch (1909) extended these 

 studies somewhat, reporting movement into the shadow of a screen even 

 when the shadow initially did not cover any part of the body. 



Working with Echinaster, Cowles (1909, 1911a,b, 1914) noted that light 

 stimulates movement toward increased illumination, a response that is 

 more rapid when the animal is intact and slower when the tips of the 

 rays are amputated. He concluded that the integument or the branchiae 

 and tube feet were very sensitive to changes in light intensity but that 

 the ocelli were important auxiliaries in oriented responses. Echinaster 

 responded to a wide assortment of mixed wave lengths (Cowles, 1911b). 

 with greater precision of orientation shown when a ray was pointed 

 directly toward a source of light. Plessner (1913) found with Asterias 

 and Solaster that the ocelli enabled a starfish to direct its movements 

 toward a slit of light or a dark object and that their destruction elimi- 

 nated these responses, although the general dermal photosensitivity 

 allowed reaction to change in intensity of light by variations in kinetic 

 activity. MacCurdy (1912, 1913) with Asterias reported the exact 

 opposite — that removal of the ocelli did not alter the ability of indi- 

 viduals to orient as normally as intact specimens. Just (1926, 1927) 



