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 discs, 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 Mierodinadae are an earlier 

 branch than the Adinetadse. 



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 paradoxa, 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 oesophagus. 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 Notommatadae, etc. 

 The jaws are not merely snapped and withdrawn. It has been seen to seize a 

 filament of Spirogyra, and leisurely chew it for a long time, the jaws all the while half 

 out of the mouth. 



Philodinadjs. 



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. Forel in the Lake of Geneva, the first record, to my knowledge, outside of Scotland. 



