176 BEPOET ON THE NUDIBRANCHIATE 



out the group are certainly very various, just as they are in Lepi- 

 doptera. One case especially is worthy of a moment's notice, viz. that 

 of the tiny Dorid, ^girus punctilucens. I have only met with one 

 example of this form as yet, but in the conditions in which I met 

 with it (see notice of species, infra) its general colour, form and size 

 were highly protective in the way of rendering it inconspicuous. 

 On a closer view, however, the sparkling blue-green spots which are 

 so characteristic of the species became evident and conspicuous. The 

 idea at once struck me that these spots must be serviceable in some 

 way when the general protective colouring has failed to conceal the 

 animal from its enemy, but of this, from lack of individuals for 

 experiments, I can adduce no proof. Further, the habits of the 

 Nudibranch itself are not at all satisfactorily known ; D'Orbigny 

 states it to live upon small species of Ulva, but though I can give no 

 conclusive evidence I am almost sure that the habit which D'Orbigny 

 observed is by no mean normal. Another case which appears to 

 me to be similar is that of Elysia viridis, which is coloured bright- 

 green and lives among green weeds. On its back, however, are a 

 number of pearly spots in regular rows, very conspicuous upon a 

 close view. I cannot help comparing them with the spots on the 

 back of j^girus punctilucens. In Elysia these spots appear to mark 

 the positions of " pouch-like mucous follicles,"'^ a fact which adds 

 to the interest of the case. I hope shortly to give an account of 

 their structure and function, and of the value to the species of the 

 markings which indicate their presence. 



I desire here to express my great indebtedness to my friend and 

 former tutor, Mr. E. B. Poulton, M.A., F.R.S.,t for his constant 

 kindness and encouragement ; also to Mr. W. Hatchett Jackson, 

 M.A., F.L.S., for the equal value of his friendship and advice ; and 

 to Mr. G. C. Bourne, M.A., F.L.S., the Director of the Laboratory, 

 for the time and facilities which he has readily granted me. I 

 must also thank Canon A. M. Norman, M.A., D.C.L., F.L.S., for 

 the help of his experience on several points, and Professor Charles 

 Stewart, M.A,, F.L.S., for information about the Fauna of Plymouth 

 Sound in previous years. 



In the report I have refrained from discussing anatomical 

 characters, since I have not been able to consult the original papers 

 and monographs of Bergh (with one or two exceptions) and Trinchese. 

 To the same cause I should wish to be attributed whatever imper- 

 fections may be found in my classification. 



* See Macalister, Introduction to Animal Morphology, part i, 1876, p. 280. 

 t I need hardly refer to the great suggestive value of Mr, Poulton's numerous papers on 

 the colour, markings, and liabits of lepidopterous larvae and pupse. 



