320 DAVID BEYCE ON 



the two teeth of the ramus, as I have shown in sketch (drawn 

 to scale from the last of three mastaces dissolved out by use 

 of sodium hypochlorite solution). That three teeth were present 

 appeared quite certain, but their relative position was very 

 obscure, and I could not be sure that the single tooth belonged 

 to the uncus and the paired teeth to the ramus, or vice versa. 

 As my material was exhausted, I could not further investigate 

 this detail. I was also unable to see definitely, first, whether 

 the single tooth was hinged or connected in any way to the paired 

 teeth, or had free and independent movement, and, second, 

 whether it was always thrust between the paired teeth or 

 whether it could also be moved forward beyond them. 



In addition to the several parts figured, I saw in this last 

 mastax two very slender rods, in length equal to about one-half 

 the manubrium. Each seemed to be attached to one of the 

 manubria near its junction with the uncus and. to pass thence 

 at about right angles towards the dorsum. I could not more 

 definitely locate them. In the mastax of Encentrum dastopis 

 (Gosse), Harring has seen slender L-shaped pharyngeal rods, 

 attached to the incus near the joint of the uncus to the manu- 

 brium. These pharyngeal rods are possibly homologous with those 

 of the mastax now described. As in many allied species, the 

 trophi are exsertile and are frequently protruded when the animal 

 is hunting about for its food. One individual which had lived 

 for two days in a trough was found on the third day to have 

 thrust forth the trophi so far that it could not get them back 

 again, and as nothing could be done to help it, it very soon died. 

 Both Milne and de Beauchamp have noted similar instances of 

 dislocation in other species of the genus. I was unable to discern 

 the brain, ovary or contractile vesicle. The latter two were 

 probably obscured by the swollen stomach and intestine. No 

 eyes were observed. 



About a dozen living examples were obtained from washings 

 of the " dry tundra " mosses (L 25). When dealt with, the 

 moss was so dry as to be friable. This new form is therefore to 

 be added to the very short list of Ploimid species, which can 

 protect themselves against desiccation. It is not known whether 

 this protection is afforded by a varnish-like secretion by the 

 alarmed rotifer as in the case of the Bdelloid species, but it seems 

 probable that such is the case. 



