498 
ZOOLOGY: AREY AND CROZIER 
a number of precise and intricate bionomic correlations result automati- 
cally from the animaFs modes of reaction, mediated by a central nervous 
apparatus which is relatively diffuse, less centralized functionally than is 
that of other molluscs; the habits so expressed determine the nature of 
the environment in which the Chiton lives. 
Full reports of these studies will be found in papers to appear in the 
Journal of Experimental Zoology, and in the American Naturalist. 
^ Contributions from the Bermuda Biological Station for Research, No. 112. 
' cf. Crozier, W. J., These Proceedings, November, 1918. 
THE NERVOUS ORGANIZATION OF A NUDIBRANCH' 
By L. B. Arey and W. J. Crozier, 
Northwestern University and University of Illinois 
Communicated by E. L. Mark, September 5, 1919 
Having in mind the important position of the moUusca with respect 
to the evolutional elaboration of central nervous organs, we have sought 
to obtain evidence permitting a more precise statement of the functional 
relations between the peripheral and the gangHonic conducting path- 
ways in a nudibranch, Chromodoris zebra. The absence of a shell in these 
animals, and certain more specific peculiarities of their construction, 
afford favorable conditions for such analysis. A full account of our 
observations is in press, to appear in the Journal of Experimental Zoology.^ 
The dorsally placed 'crown' of gills comprises in Chromodoris about 
12 distinct plumes arising from a ridge abnost surrounding the anal 
aperture. Each plume may contract independently. All of the plumes 
may also contract simultaneously, and the whole gill-crown may be con- 
cealed within a collared pocket. During the day-time, and under cer- 
tain conditions of alkalinity and temperature in the seawater,^ the plumes 
are extended. If a plume be lightly touched at one point, the common 
orm of response is constriction at that level, resulting in a sKght swaying 
of the plume. More vigorous stimulation Kkewise leads to this locally 
confined unsymmetrical contraction, which however is now seen to 
spread distally from the site of activation, as a collapse and shrivelling 
of the plume, and is also accompanied by the downward pulKng of the 
entire plume through the traction of muscles situated in the basal tissue 
of the gill-crown. Still stronger activation induces longitudinal shorten- 
ing of the plume, both distally and proximally to the point of stimula- 
tion, and in the basal tissue.^ 
