Defence among certain Medusa. 349 



podidse have no cystons or similar excretory organs, nor has 

 the function of excretion yet been referred in them to any 

 special organs. Is it possible that the discharge of coloured 

 matter from the pigment-cells of the bract of Agalma is also 

 a method of excretion? and is it the same as that of the cystons 

 of Forskalia'? It seems to me improbable that we have to 

 deal with excretions only in this case, although we may have 

 an instance of a novel means of protection, which is in part 

 accomplished by the discharge of the excretion in Forskalia. 

 Upon this theory, however, we need much more light, which 

 can best come from more observation. 



It is legitimate to conclude that the discharge of a highly 

 coloured fluid by the scales of Agalma is in part a means of 

 protection for the Medusa, and it would seem natural to con- 

 nect it with the function of excretion ; but we know so little 

 about the character of the excretions and the manner in which 

 they are produced in Medusaj, that at present we can hardly 

 definitely ascribe the special function to these glands. Pos- 

 sibly similar glands are found in other Physophores, and the 

 excretion has not been recognized from the fact that it is not 

 so highly coloured as in Agalma Clausi and Forshalia. The 

 discharge of this fluid from a living animal, if it take place 

 without rupture of the wall of the scale, would imply special 

 excri'tory openings somewhere on the bract ; and one is 

 tempted to search for such openings, if they exist, on the 

 distal tip of the scale, when they would be homologous with 

 the excretory openings known to exist on the bell-margin of 

 certain Hydromcdusa^, as Metschuikoff and others have 

 shown. 



If we accept tlie theory that the discharge of a coloured 

 fluid is a method of defence, the question arises. How is that 

 defence accomplished ? Does the fluid darken the water in 

 the immediate vicinity of the Medusa which possesses this 

 power and in that way conceal it from its foes, as in the case 

 of the Cephalopoda ? or does it serve, as is possibly the case 

 ■with the rattle of the rattlesnake, to warn away its enemies ? 

 May it not even bewilder its prey and thus be rather a means 

 of capturing its food than of self-protection ? Has it possibly 

 a poisonous nature fatal to its prey or foes? Our knowledge 

 of its nature is all too small to give us an answer to these 

 questions. Its bright colour would indicate that even if it is 

 poisonous this is not its only property, or its sole function 

 that of killing its enemies or prey. The ability to change the 

 colour mentioned in Geratocymha by Dr. Chun might come 

 in the same category as a similar power in tishes and Cepha- 

 lopoda. In that case we might have a kind of cutaneous 

 Ann, & Mag. N. Hist. Ser. 6. Vol. iv. 25 



