206 Prof. F. J. Bell on the Arrangement and 



of the hand pale except the outer finger, while the lower side 

 of the hand has the colour of the outer side of the arm. 

 Boulenger* seems to be the only author who has hitherto 

 understood the hand in this animal correctly, having had the 

 opportunity of observing it in the living state ; he has noticed 

 the position of the hand with the fingers superposed, the 

 inner fingers only touching the ground, and the colourless 

 condition of the inner {i. e. upper) side, though he has not 

 remarked that in the latter respect this frog resembles most 

 others. A most interesting addition to the brief biological 

 account given by Boulenger we owe to Leslie f, who states 

 that X. la'vis is essentially aquatic in its habits, that it, 

 unlike other frogs, feeds only in the water and forces its prey 

 into its mouth by means of its hands, which act as a pair of 

 claspers { ; its mode of locomotion on land is by difficult and 

 awkward crawling and leaping, and when at rest it never 

 assumes a sitting posture, and the back never appears humped. 

 Even Leslie has made a slight mistake, saying that in the 

 breeding male " the palmar surface and inner side of the fore- 

 arm acquire a black horny layer ; " this structure is found on 

 the back of the hand, as is the case with our frogs and toads. 



XXIV. — On the Arrangement and Inter-relations of the Classes 

 of the Eclmwdermata. By Prof. F. Jeffkey Bell, M.A. 



Having recently had to attempt the formulation of exact 

 diagnoses of the various living classes of the Echinodermata, 

 I have been led to consider closely the claims of the present 

 current classification into Pelmatozoa and Echinozoa. The 

 moment we look at the matter from the phylogenetic point of 

 view we find ourselves involved in a very maze of difficulties. 

 Are the stalked derived from the unstalked forms or vice 

 versa "? If the group Echinozoa is natural, how intimate are 

 the relations of the Hoh^thurians to the other skeleton-bearing 

 forms with remnants at least of a calycinal area ? What are 

 the points, other than the non-fixed condition, which unite 



* Proc. Zool. Soc. Lond. 1887, p. 563. 



t " Notes on the Habits and Oviposition of Xenopus Icevis,'' Proc. Zool. 

 Soc. Lond. 1800, p. m. 



\ Perhaps the great process on the ceutrale, the process x, &c. are 

 connected with this peculiar use t)f the hands ; and it i.s probable that 

 we sliall some day learn that Pipa behiives in a similar way. 



