Mv. J. Alder on Euplocamus, Triopa and Idalia. 263 



E. Inciniosus. Upon tliis I would remark, that tlic function here 

 attributed to the lateral appendages of E. croceus is jjrobably 

 correct, yet not so self-evident but that it would be desirable to 

 brinp: tliem to the test of the microscope, — a mode of investigation 

 which this distinguished naturalist ajjpears to hold in slight 

 esteem. With regard to the latter part of the observation, which 

 im])lics that if the appendages of E. cruceus are branchial those 

 of E. {Idalia) laciniqsus are so also, I cannot assent to it. Indeed 

 Dr. riiilippi would appear to have some doubts upon the point, 

 for, referring to his descriptions, I find that these processes are 

 called " hranchice " in E. croceus and E. ramosus ; in /. cinigera 

 " branc/iiaV (with a query); and in /. laciniosa they are simply 

 called " cirrhi," the term branchise being properly reserved for 

 those processes surrounding the vent. 



The animal examined by Professor Forbes was not one of the 

 Sicilian species, but the only British species referred to the genus 

 by Dr. Philippi (and which is also the type of Dr. Johnston's 

 genus Triopa), viz. Doris clavigera of ]\Iiillcr. 



Dr. Philippi next asks, whether it is a fact that all the organs 

 serving for respiration are fm-nishcd with vibratile cilia, and says 

 he can scarcely believe that the branchiiie of Eolis are ciliated, 

 because they appear not to differ in anything from the lateral ap- 

 pendages of Euplocamns. It is unfortunate that the learned au- 

 thor has not been in the habit of using a microscope in the exa- 

 mination of these animals, as, had he done so, he could imme- 

 diately have satisfied himself of the fact, and thus have avoided 

 the fUsadvantage of offering an opinion in opposition to the tes- 

 timony from observation not only of Professor Forbes, but of se- 

 veral other naturahsts who have lately \\Titten on the subject. 



To the question, whether the branchial organs are always 

 ciliated, the concurring observations of anatomists will, I think, 

 justify a reply in the affirmative ; at least I am not aware of any 

 case to the contrary. The absence of vibratile cilia therefore may 

 be taken as a fair presumption that an organ is not adapted for 

 respiration. Their presence however does not always imply that 

 function, as several other delicate tissues in the animal ceconomy, 

 especially when cm-rents are required, are well knoA\'n to be 

 ciliated. 



The next question asked by Dr. Philippi is, whether the genus 

 Triopa is really the same as his Euplocamus ; and he infers from an 

 observation of mine that " Triopa Nothus of Johnston is probably 

 a Pohjcera," that Triopa and Polycera are the same, and as Po- 

 hjcera is different from Euplocamus, we must have very lax no- 

 tions of what constitutes a genus. " Cum iis, qui tales differentias 

 ad distinctionem generum non valere putant, litem habere nolo ; 

 sed iis adsentire non possum." 



