[Reprinted from THE AMERICAN NATURALIST, Vol. LI., December, 1917.] 



FUSION OF 'RHINOPHORES" IN CHROMODORIS 1 



THERE have been found during the present spring nine spec- 

 imens of the nudibranch Chromodoris zebra Heilprin which 

 form a series exhibiting an interesting gradation in the degree 

 of coalescence of the "rhinophores." The animals were each 

 of average adult size, 10-12 cm. in length. In none of these 

 cases was there any evidence that the structural variations had 

 resulted from injury. In the period over which these individ- 

 uals were obtained there were also collected about 1,000 normal 

 specimens of the same species. These figures give, however, no 

 precise idea of the relative frequency of "rhinophore" variation, 

 because a larger number of specimens had been collected in 

 previous years without any occurrence of these variations being 

 observed. 



I I 



o o 

 6 6 

 O O 



PIGS. 1-6. Outlines of anterior ends of Chromodoris zebra Heilprin, show- 

 ing increasing degrees of fusion of the " rhinophores." Fig. 5, frontal view : 

 the rest, dorsal aspects. Fig. la, the normal condition ; Fig. Ib, variation in the 

 edges of the " rhinophoral" collars of three individuals. 



The bases of the two "rhinophores" of C. zebra are, as in 

 other Dorids, normally surrounded by well developed individual 

 cylindrical collars. The distal termination of a collar is usually 

 circular in outline, but occasionally pointed at one side (Fig. 

 1). In two specimens the "rhinophoral" collars were closely 

 approximated, after the fashion outlined in Fig. 2. Three spec- 

 imens were found in which the "rhinophoral" collars, and the 

 depressions into which the ; ' rhinophores" are separately re- 

 tracted when stimulated, had completely fused (Fig. 3). In 



i Contributions from the Bermuda Biological Station for Research, No. 75. 



