468 



Mr. G. H. Grosvenor. 



[Nov. 3, 



approximately the same range of variation in size ; the colour in both 

 is a beautiful translucent violet, with brick-red or carmine diverticula- of 

 the gastric gland showing through the integments of the cerata. I have 

 no direct evidence as to what hydroids they frequent, but I have on 

 several occasions received specimens of the two species together, and 

 the evidence of their nematocysts given in the following table, leaves 

 no doubt that their food is the same. This is probably, therefore, a 

 case of mutual mimicry, since both species are protected (by mucous 

 glands and nematocysts). 



The nematocysts figured in fig. 6 I have not as yet been able to 

 find in any Ccelenterate ; they are apparently those which Bergh 

 considers " ganz eigenthiimliche." But I think the evidence is scarcely 

 in favour of this view, even when this case is considered by itself. 

 For, as shown above, these nematocysts are found in about half of each 

 of these by no means nearly related species ; while, on the other hand, 

 I could not find a trace of them in two specimens of Cor. Scacchiana 

 or five Cor. lineata. I have not had an opportunity of examining any 

 other species of Flabellina. 



3. Whenever it is known what particular Coelenterate an ^Eolid has 

 been feeding on, the nematocysts of the two are found to be identical. 



Strethill Wright gave four instances of this and Glaser has given 

 another. I may add a few more. 



As mentioned above, the dSolidiadce proprice of Bergh have usually 

 typical Actinian nematocysts, and many of them are known to feed on 

 Actinians. An Ae. papillosa found at Plymouth among stones on 

 which the common red Anemone was abundant, had nematocysts 

 indistinguishable from the latter. An ^olidiella Alderi dredged at 

 Plymouth had nematocysts exactly like those of Sagartia (fig. 6). It 

 is known to feed on a species of Sagartia (see Garstang (9)). Mr. Garstang 

 told me that he had been struck by the similarity of the nematocysts 

 of these two animals some years ago, and showed me drawings he had 

 made at the time. 



