170 MR JAMES MURRAY ON 
toes seem to me adaptive characters. As it feeds by biting, it does not need discs; and 
as it has not dises, and therefore cannot swim, it would be under a disadvantage without 
powerful toes. 
The close correspondence to the Philodinoid type of structure in almost all but the 
corona and jaws, especially in the rostrum and foot, suggests that the peculiarities of 
Microdina are due to retrogression from Philodina. On the other hand, the transition 
from a fully developed Philodine to Microdina is difficult to imagine, because the short 
gullet and protrusible jaws must be completely acquired before they would be 
serviceable. 
Since the jaws approximate to the central type of the whole class (see GossE on the 
manducatory organs (17)), and the short gullet and protrusible jaws are also frequent 
throughout the Ploima, there is some ground for supposing that the Philodinoid corona 
never has been developed, and that the mouth and jaws are more primitive characters 
surviving from a common Bdelloid ancestry, from which the Microdinadee are an earlier 
branch than the Adinetadee. 
Such conclusions are little more than conjectures, and the discovery of other links 
may prove that the affinities are quite other than I have supposed. 
Microdina paradowa, Murray.* (Plate IV. fig. 17.) 
Since the species was described (39), it has been found frequently in lochs and 
streams. It has thus been possible to learn more about its structure and habits. 
The characteristic red mass in the head has been definitely ascertained to surround 
the cesophagus. Small examples, which I take to be young, lack this red mass, and 
are colourless throughout. 
The very short gullet was early pointed out as an important character by Mr Bryce 
(to whom I am greatly indebted for assistance in elucidating the structure of this 
anomalous animal). The meaning of the short gullet is now understood. The jaws 
can be completely protruded, as is done by many predatory Notommatade, ete. 
The jaws are not merely snapped and withdrawn. It has been seen to seize a 
filament of Sperogyra, and leisurely chew it for a long time, the jaws all the while half 
out of the mouth. 
PHILODINAD. 
The three genera of this family which occur in the lochs are redefined to permit of 
a more natural arrangement of the numerous species. The eye-spot is given up as a 
generic character. The character of the toes is the most important feature used in the 
classification ; the mode of reproduction is made use of, for want of anything better. 
Whatever objection there may be to using the mode of reproduction, unquestionably it 
characterises natural groups in the Bdelloids. 
* Recently collected by Prof. Forex in the Lake of Geneva, the first record, to my knowledge, outside of Scotland. 
