1886.] DURING THE VOYAGE OF H. M.S. 'challenger/ 113 



is represented by a single specimen, which was dredged in the Pacific 

 Ocean at Station 218, in 1070 fathoms of water. It is a large 

 Isopod, measuring upwards of two inches in length, and agrees in 

 most particulars with such genera of the Cymothoidae as j^ga ; but 

 at the same time it presents certain remarkable peculiarities analo- 

 gous to those exhibited by the aberrant genus Bathynomiis lately 

 described by Prof. A. Milne-Edwards from deep water in the North 

 Atlantic. M. Milne-Edwards's preliminary account of Batliynomus 

 was communicated to the French Academy', and a translation 

 of his note has appeared in the Ann. & Mag. of Nat. Hist." 

 Apart from its huge size, the most remarkable feature in the 

 organization of Bathynomus is the great development of branchial 

 organs : " it appears," says M. Milne-Edwards, " that the respiratory 

 apparatus of an ordinary Isopod is insufficient to supply the physio- 

 logical needs of Bathynomus, and that the development of special 

 organs of a greater functional power has been rendered necessary. 

 The abdominal limbs, which usually in this group constitute the 

 sole branchial apparatus, in Bathynomus only serve the function of 

 a covering to the gills which lie beneath them." The gills of this 

 Crustacenn are in fact represented by a series of complicated branched 

 outgrowths of the body-wall in the ventral region of the abdomen. 

 The same end is attained by the Crustacean, which forms the sub- 

 ject of the present remarks, in a different manner. Instead of a 

 development of accessory respiratory organs, Anuropus (as I may term 

 the genus from its chief structural peculiarity) exemplifies one 

 extreme of the Isopodan type, in that all the abdominal appendages 

 are converted into respiratory organs ; the increase of respiratory 

 surface is thus attained by an exaggeration of a structural character, 

 which is common to all the members of the family, and which indeed 

 is an important basis of distinction from other famihes of Crustacea. 

 In all the members of this group more or fewer of the abdominal 

 limbs are soft foliaceous appendages, which permit of an easy 

 exchange of gases between the contained blood and the sea-water. 

 There is no instance, however, among the Isopoda in which all the 

 abdominal appendages are similar, functioning as respiratory organs, 

 except in this deep-sea genus Anuropus. Bathynomus, as regards 

 the uropoda, is quite a typical Isopod ; these ap})endages form a 

 pair of swimming-feet as they do in the other Cymothoidae . 



The modifications of the terminal pair of abdominal appendages or 

 uropoda serve to divide the Isopoda into natural families, which 

 prove to be allied in other particulars ; and some stress, therefore, 

 from a classificatory point of view, should perhaps be laid upon the 

 fact of their modification in Anuropus, though it is always open to 

 question how far a purely adaptive character is of value. Since the 

 present genus agrees with the Cymothoidae in the general form of 

 the body, in the number of free abdominal segments, and in fact in 

 all essentials, it would perhaps be hardly permissible to remove it 



^ ' Comptes Rendus,' Jan. 1879. 

 - Ann. & Mag. Nat. Hist. 1879 (vol. iii.), p. 241.. 



3 There is a figure of Bathyiiomm in an interesting work recently published 

 by M. Filhol and entitled ' La vie au fond des mers,' Paris, 1885. 



Proc. Zool. Soc— 1886, No. VIII. 8 



