58 W. A. HERDMAN. 



tory organs and that their chief function is by their varied 

 shapes and colours to enable the animals to assume protective 

 or warning appearances as may be found best suited to their 

 surroundings and mode of life. 



It is still necessary for the satisfactory establishment of this 

 theory that I should have some more definite experimental 

 grounds for my opinion that such forms as Doto and Dendro- 

 notus are edible^ while Eolis is distasteful to (say) fishes, and 

 I have lately arranged a series of experiments which will be 

 conducted in the fish-tanks of the aquarium here, with the 

 kind assistance of Mr. T. J. Moore, the curator of the Liver- 

 pool Museum. We have just commenced observations, and 

 have got satisfactory results so far with eight species of shore 

 fishes, but at this season it is almost impossible in this neigh- 

 bourhood to get Nudibranchs in any quantity. As soon as 

 more material can be obtained the experiments will be resumed, 

 and I shall give a detailed account of the results when suffi- 

 cient evidence has been accumulated. 



Summary. 



1. In Doris there are true branchiae and no cerata. In 

 Ancula both branchiae and cerata are present. In Tritonia 

 and Dendronotus there are cerata, but no true branchiae. 

 In Ancula, Tritonia, and Dendronotus the cerata, whether 

 simple or branched, large or small, are merely processes of the 

 body-wall (parieto-cerata) and contain no special organs or 

 structures. 



2. In Doto and Eolis there are no true branchiae. The 

 cerata (hepato-cerata) are large, and contain extensive hepatic 

 diverticula. 



3. In Eolis the hepato-cerata contain also cnidophorous 

 sacs which communicate on the one hand with the distal end 

 of the hepatic caecum, and on the other with the exterior at the 

 apex of the ceras. 



4. Morphologically, all the forms of cerata are probably 

 epipodial processes. 



