290 W. J. CROZIER AND LESLIE B. AREY 



The eyes of Chromodoris are small and are situated beneath 

 the skin. They are in close relation with the supraoesophageal 

 ganglionic mass, being connected therewith by means of short 

 slender nerves running to small optic ganglia (Smallw^ood and 

 Clark, '12). Externally, the region of their location in the nor- 

 mally extended animal is indicated by two clear-blue areas 

 immediately posterior to the 'rhinophores' (fig. 1). In nudi- 

 branchs found by previous test to be actively photopositive, these 

 regions were cauterized with a hot needle. Subsequent experi- 

 mentation showed that the photopositive behavior of these in- 

 dividuals w^as in no way affected by the operation. A scar-Uke 

 formation was produced, accompanied by some local puckering, 

 together with a deep dorsal constriction and insinking of the 

 body at the level of the burn. The movements and general 

 behavior of the animal are in no way altered. "^ 



It is doubtful if operations of this type really interfere with the 

 possible functioning of the eyes. Nevertheless, when tested with 

 small areas of illumination, even when the light was very intense, 

 the normal Chromodoris w^as found to be reactive at the anterior 

 end, in the region of the eyes; the posterior end was non-reactive 

 to sunlight concentrated with the aid of a lens of 30 cm. focal 

 length when the heat rays had been eliminated. We are not in 

 a position to decide as to whether the eyes are photosensitive 

 (for they are not easily approached for excision tests) , nor whether 

 there are anterior integumentary receptors independent of the 

 eyes. The 'rhinophores' are not sensitive to light. 



The gill plumes, however, — more or less completely retracted 

 in the dark, as already described, — become fully expanded when 

 the region of the branchial collar alone is illuminated. They do 

 not become extended, it would appear, when only the anterior 

 end of the animal is illuminated. The latter 'test is difficult to 

 make because anterior illumination induces active creeping. 



^ The region of the skin bearing the eye spots has also been removed in a 

 number of cases, exposing the body cavity. Animals so prepared are photo- 

 positive; they live for a week or more and seem in no way greatly incommoded 

 by the operation. Through such a window in the skin it was attempted to 

 stimulate the eyes directly, with a small spot-light. It seemed that the region 

 of the eyes was sensitive to light, but the experiment should be repeated. 



