216 J. MURRAY ON PHILODINA MACROSTYLA, EHR., 



oblong eyes, and it appears to depend on the point of view which 

 appearance they have. P. spinosa has no eyes. Eckstein (5) and 

 Janson (13) found the eyes always oval, never round, in P. aculeata. 



Jaws. — The two jaws together form an almost circular body. 

 Each jaw has a thick brown border, and bears three equal teeth. 

 Ehrenberg described both P. aculeata and P. macrostyla as having 

 three teeth in each jaw. Dr. Burn (3) and Mr. Western (19) 

 suppose this to be an error as regards P. macrostyla, and that the 

 usual arrangement is three teeth in one jaw and two in the other. 

 In my experience there are normally three equal teeth — very 

 rarely one tooth in each jaw is smaller, as in the typical Philodina. 



Bryce (2) in 1893 says that he found the dental formula to be 

 3/2 in two examples of P. spinosa. 



Rump and Foot. — The posterior portion of the body, considered 

 by the earlier naturalists as the foot, is now regarded as consisting 

 of two portions, that part after the anus being now alone defined 

 as the foot. I have proposed the name rump for the narrowed 

 portion between the central trunk and the anus. This usually 

 has only two segments, the preanal and the anal ; but may 

 include the fourth central. 



In the viviparous Philodinadae the rump is separated from the 

 central trunk by a sharp constriction. The homologies of the 

 segments of the rump are here rather obscure. I am inclined to 

 think that the constriction occurs between the third and fourth 

 central segments, and that it is this segment which forms the first 

 expansion of the rump and bears the last pair of spines in the 

 spiny forms. 



When seen well extended this part of the body has a nodose 

 appearance with three or even four nodes. 



Foot. — The foot consists of four joints. The first is longer 

 than the second, which is very short. The third, or penultimate 

 segment, which bears as a rule the spurs, is short. It is swollen 

 at the base, then forks, forming two rounded cushions, which 

 support the spurs (Fig. 24). 



Spurs. — The spurs are always very long and slender, relatively 

 longer than in other Bdelloids, except perhaps Rotifer neptunius, 

 Milne, and Rotifer actinurics, Ehrenberg. 



