<38 D. BRYCE ON A NEW CLASSIFICATION OF THE BDELLOID ROTIFERA. 



escaped observation, as may be judged from Elirenberg's figure 

 of the stomach of Philodina collaris (4), and from his description 

 of that organ both in that species and in his Callidina redivira. 

 Oosse, in his turn, observed some pecuHarities about the stomach 

 of Callidina bidens (19) which he did not lightly interpret. 

 Lastly, Milne (18) in his descriptions of species discovered by him 

 drew attention in several cases to the remarkable habit of 

 moulding the food into pellets, which is universal amongst species 

 whose stomach-structure dev-iates from the customary form in 

 the manner now to be pointed out. 



Briefly stated, the distinction made consists in the proportion 

 of the cavity of the inner or lining membrane of the stomach 

 to the cavity of the outer or enclosing membrane, and it is 

 constantly associated with a difference in the method of digestion 

 and with other structural differences, which, if not of great value 

 in themselves, indicate clearly enough that the difference in the 

 stomach-structure is one that goes a long way back in the 

 evolution of the Bdelloida. Makina^ use of this distinction I have 

 divided the genera of the Philodinidae into two Sections : 



A. Lumen of stomach relatively wide, or bag-like ; food 



usually in pellets ; upper lip usually entire ; oviparous. 



B. Lumen of stomach relatively narrow, or tube-like ; food 



particles free, never agglutinated into pellets ; upper 

 lip usually bilobed or divided ; oviparous or viviparous. 



In the genera of Section B the inner tube is very much 

 narrower than the outer, the interspace being occupied by a finely 

 granulated digestive fluid, having a frequent admixture of fat- 

 particies. In the genera of Section A the inner tube is almost as 

 wide as the outer, and the granulated fluid is usually scanty or 

 apparently absent. Again, when the lumen is tube-like one 

 frequently finds ciliary action visible either in the stomach or in 

 the intestine. In my experience such action is never seen when the 

 lumen is relatively- wide. The moulding of the food into pellets, 

 which is universal among the species of Section A, has never 

 been detected in any species with a relatively narrow lumen. 



It is not to be expected that among so many species all 

 should conform with equal fidelity to the distinction made 

 between the relatively narrow and the relatively wide lumen of 

 the stomach. Notably in the genus Rotifer many species have 



