THE NAUTILUS. 103 



(Reprinted from THE NAUTILUS, Vol. XXX., January, 1917.) 



THE NATURE OF THE CONICAL BODIES ON THE MANTLE OF CERTAIN 



NUDIBRANCHS. 



BY W. J. CROZIER. 



Contributions from the Bermuda Biological Station for Research, No. 57. 



A study of the supposed ' ' warning ' ' coloration of brilliantly 

 pigmented nudibranchs as represented by Chromodoris zebra 

 Heilprin, has incidentally made clear the previously unknown 

 significance of the "white conical bodies" which occur on the 

 posterior ventral surface of the mantle of this species and give 

 it a beaded appearance. Since white nodular structures of a 

 presumably similar character have been noted upon the mantle 

 edge of other tropical nudibranchs, the function of these organs 

 as worked out in 0. zebra is probably identical among all the 

 species in which they occur. 



The bodies in question are in fact glands, which store a spe- 

 cial secretion concerned in protecting the nudibranchs from the 

 attacks of preying enemies. They are, in a functional sense, 

 comparable to the repugnatorial glands of the littoral pulmonate 

 Onchidium, although their mode of action is different. They 

 occur, usually 5, 6 or 7 in number, immediately over the 

 "tail." In some instances 10, 12, and even as many as 19, of 

 these organs have been noted. The manner of their distribu- 

 tion strongly suggests that 5, and in some cases 7, specialized 

 regions exist which give rise each to one of the conical bodies. 

 The central gland of the 5 or 7 is situated in the median plane 

 of the body. It is significant that the increased number of the 

 organs, when they exceed 7, is usually (if not invariably) asso- 

 ciated with some injury, such as would be occasioned by the 

 bite of a fish, which has removed a portion of the gland-forming 

 area of the mantle. 



Not all the bodies on a single animal are of the same size, one 

 or more being sometimes quite minute. The definite pattern 

 according to which they are arranged is preserved even in cases 

 where one or more of the glands is totally suppressed. 



