THEIR RANK. ] 9 



resemblance in the curious, doubly pectinated spines on the 

 anterior limbs of Mysis (allied to Phyllosoma*), and on 

 those of many Cirripedes : these several latter resemblances 

 may be small, but certainly I do not believe that they are 

 accidental. Now the little group of Crustaceans, which 

 includes Fhyllosoma, &c, has lately been placed, by 

 Milne Edwards, as a satellite amongst the Macrourous 

 Podophthalmia ; it leads into the Stomopoda, and likewise, 

 as has been noticed by many authors, into the sub-class 

 Branchiopoda, which latter sub-class is considered by Mr. 

 Dana as only a part of the Entomostraca ; this group, there- 

 fore, exhibits affinities radiating in several directions, and 

 amongst these lines of relationship, one more must, I believe, 

 be added, plainly directed towards the Cirripedia. 



One naturally wishes to ascertain how far Cirripedia 

 are highly or lowly organised and developed ; but in all 

 cases this, as it seems to me, is a very obscure enquiry. 

 Mr. Dana considers that, in Crustacea, the greater or less 

 centralisation of all the appendages round the mouth is the 

 main sign of high development ; on this view, the anterior 

 part of a Cirripede, from being so much elongated, must 

 be considered as very low in the scale ; the whole posterior 

 part of the body, on the other hand, is, in ordinary Cirri- 

 pedes, brought close to the mouth ; but this is effected by 

 the abortion of the seventh and eighth segments of the 

 cephalo-thorax and of the whole abdomen, and so, I presume, 

 would not, in Mr. Dana's estimation, raise the class much 

 in the scale. Von Baerf considers that the perfection of the 

 type of any animal is in relation to the amount of " morpho- 

 logical differentiation" which it has undergone ; on this view, 

 Cirripedes ought to stand high in the scale, for they differ 

 much morphologically from the type of the class to which 

 they belong ; as indeed is shown by the long time that elapsed 

 before their true position, namely amongst the Crustacea, was 

 even suspected ; but something more must, I think, be added 



* M. Martin St. Ange ('Memoire surTOrgan. des Cirripedes,' 1835, extrait 

 des ' Savans Etrangers,' tom.vi) has compared the mouth of Lepas with that of 

 Phyllosoma, and has given comparative figures ; but the resemblance is founded, 

 I believe, on quite false homologies. 



f English Translation, in ' Scientific Memoirs,' 1853, vol. i, p. 228. 



