i 



of the Division Hv'perina. 15 



that the latter is the result of development superinduced by pe- 

 culiar conditions. Thus, several genera, the young of which start 

 from a common type, undergo changes most opposite to each 

 other in order to fulfil with advantage the conditions under which 

 they are placed. 



Our knowledge of the habits of the Hyperina is very limited. 

 They have mostly been found dwelling in the gill- cavities of 

 Medusse; but the few specimens of Rhabdosoma of which the 

 habitat has been recorded were taken swimming freely in the 

 ocean. Whether or not this may be the habit of this very cu- 

 rious creature, I cannot say ; but Platyscelm, Brachyscelus, and 

 other allied genera are certainly animals which have undergone 

 a deterioration of character, and the great alteration of parts is 

 such as their permanent condition may have required. The 

 small eyes of the type are produced into monstrous organs in 

 order, we may assume, to make up for the depreciation of the 

 light that reaches them through the transparent animals in the 

 cavities of which they take up their adode. The basa of some 

 of the pereiopoda are developed to a monstrous degree, and at 

 the expense of the remaining joints, inasmuch as the walking 

 appendages are not required by animals that are not in a posi- 

 tion to use them ; while the great squamiform basa of the third 

 and fourth pairs protect the entire range of ventral organs, as 

 well as the ova and young. 



The adult animals having departed from the typical character 

 of Amphipoda, we must look for their nearest aUies in the order 

 through the relation which their young may hold with the more 

 aberrant forms. This link is certainly to be found to exist in 

 Phoxus and other genera of the subfamily Phoxides — a circum- 

 stance that points out to us a necessary emendation in the 

 classification of these animals. 



EXPLANATION OF THE PLATES. 

 Plate L 



Fig. 1. Vibilia Edwardsii, female adult. 

 Fig. 2. Ditto, young. 



b, anterior antennae ; c, posterior ditto ; h, first pair of gnatho- 

 poda ; t, second pair of ditto ; k, I, first and second pairs of pe- 

 reiopoda ; m, third pair of ditto ; n, fourth pair of ditto ; o, fifth 

 pair of ditto. 

 Fig. 3. Oxycephalus piscator. 



Fig. 4. Rhabdosoma IVhitei : b, anterior antennae ; d, mandible ; h, first 

 pair of gnathopoda ; »", second pair of ditto. 



Plate IL 



Fig. \. Brachyscelus crusculum, female adult. 

 Fig. 2. Ditto, young. 



b, superior or anterior antennae ; g, maxillipedes ; h, first pair 



