104 THE NAUTILUS. 



edge of other tropical nudibranchs, the function of these organs 

 as worked out in G. 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. 



Each of the glands is provided with a pore. In rare cases 

 two pores have been found upon a single gland. The pores are 

 surrounded by a sphincter. When Chromodoris is violently 

 disturbed in any way, its consistent reaction is to withdraw the 

 gills and rhinophores, to erect the lateral edge of the mantle, 

 and to turn under, ventrally, the posterior part of the mantle 

 bearing the glandular organs. At the same time the glands 

 become turgid, through the contraction of their muscular in- 

 vestment, the pores being then more prominent. If the irritat- 

 ing stimulation is continued, there issues from the pores of one 

 or more of the glands a white creamy secretion, which is not 

 dissolved by sea water. It is composed mainly of globules of 

 an oily substance. The secretion is not acid, but is neutral to 

 litmus. 



When the glands are stimulated individuall)' with induction 



