The Mid-Winter Meetirjgs. 193 



it seems to be in all rays. In no ray do the cerebral protrusions remain unconjoined 

 as in some sharks; but, paradoxically, in no ray is there, as in several sharks, so 

 nearly a complete obliteration of the evidence of their primary independence. 

 Under "Methods" may be enumerated: (l) The need of well-preserved brains 

 of all species; (2) maintaining the natural contours, especially of thinner parts, 

 by injecting the preservative into the cavities; (3) making solid injections of the 

 cavities; (4) exposing brains with a "shoe-knife," obliquely shortened; (5) explor- 

 ing with the "syringotome" or canaliculus knife; (6) the use of sheets of uniform 

 size, say 35 x 45 cm., upon which, in a manner permitting change, are drawn out- 

 lines of the animal and of its characteristic parts, especially the brain; such sheets 

 may be arranged and rearranged upon the wall so as to facilitate research and 

 exposition to small classes. 



An Experimental Study of the Image- Forming' Powers of Various Types of Eyes. 



By Leon J. Cole, Rhode Island A giicultural Experiment Station, Kingston, R.I. 



The responses of certain phototropic animals to two areas of light of different 

 size, but of equal intensity, were used as criteria in drawing inferences as to the 

 image-forming powers of their eyes. To one side was a ground-glass, lighted from 

 behind, which gave an evenly illuminated area 41 cm. square. To the other side 

 was practically a point of light; but at the position midway between them, where the 

 experiments were performed, the intensities of the two lights were equal. Eyeless 

 forms (the earthworm was used) turned practically an equal number of times 

 toward each light, showing no power of discriminating between them. Animals 

 with "direction eyes" were but little better in this respect (e. g., Bipalium, Oniscus, 

 larva of Tenebrio). On the other hand, animals with well-developed "compound 

 eyes" (Vanessa, Ranatra) and "camera eyes" (frogs) discriminated readily, posi- 

 tive animals turning much more often to the large light, and negative animals 

 more often to the small. This discrimination was taken as evidence of image- 

 formation by the eyes. Frogs (Acris gryllus) with the skin covered but eyes exposed 

 reacted like normal frogs; without the use of the eyes their responses corresponded 

 to those of the earthworm. 



We have th\is a physiological test of the image-forming powers of the eyes, and 

 in these experiments it corroborated in the main inferences which would be drawn 

 from a study of the structure of the eyes in question. 



The Influence of Direction vs. Intensity of Light in Determining the Phototropic 

 Responses of Organisms. By Leon J. Cole, Kingston, R. I. 

 The large land planarian, Bipalium kewense, was the principal animal experi- 

 mented with. Its responses were first tried to shadows from a light directly 

 overhead, /. e., non-directive. It was then tested in a partial shadow, a strip of 

 less intense light in an area of more intense illumination. In this case all the light 

 came from one direction, namely, horizontally from one side. Although strongly 

 negative, the worms would crawl directly toward the light in the partial shadow 

 rather than turn out into the greater intensity. A similar result was obtained 

 with the earthworm (Allolobophora foetida). In these experiments Bipalium and 

 Allolobophora appeared to respond to intensity alone, regardless of the direction 

 of the impinging light. 



