STRUOTUREj ETC., OF CERATA OP NUDIBRANCHS. 57 



its rich reddish-brown and yellow markings, is a handsome and 

 most conspicuous object, but I have frequently found it 

 amongst masses of brown and yellow zoophytes (coarser forms 

 such as Sertularia abietina and Hydrallmania falcata) 

 and on purplish-red seaweeds, where it was very completely 

 protected from observation and I did not for several seconds 

 recognise what I was looking at.^ 



Now, these are all cases where the colouring is protective, 

 and I have no doubt there are many other similar instances to 

 be found amongst the Nudibranchiata,^ but the species of 

 Eolis appear to belong to a different category. They are 

 noted for the very brilliant hues of their cerata and they are 

 always conspicuous, so far as I have noticed, even in their 

 natural conditions. 



Then, again, the species of Eolis are rarely found hiding in 

 or on other animals ; they are not shy, and they are active in 

 their habits — altogether they seem rather to court observation 

 than to shun it. When we remember that the species of 

 Eolis are protected by the numerous stinging-cells in the 

 cnidophorous sacs placed on the tips of all the cerata, and that 

 they do not seem to be eaten by other animals, we have at 

 once an explanation of their fearless habits and of their con- 

 spicuous appearance. The brilliant colours are in this case of a 

 warning nature for the purpose of rendering the animal pro- 

 vided with the stinging cells noticeable and easily recognisable. 

 It is, of course, important for the soft-bodied Nudibranch that 

 it should be not only disagreeable to taste but also as con- 

 spicuous as possible, in order that it may not run the risk of 

 being tried by voracious animals. An experimental snap from 

 a fish might cause the death of the Nudibranch even though it 

 was immediately rejected as food. 



These, then, are the grounds upon which I base my view 

 that the cerata from their structure cannot be important respira- 



' Professor Giard finds it at Wimereux amongst red seaweeds of the genus 

 Callithamnion. 



2 Such as the interesting cases of Hermaja bifida and H. deudritica, 

 described h;j Garstaug, loo. cit., p. 191. 



