A Rotifer New to Britain. 51 



is made to open, by the bending forward of the head towards 

 the ventral aspect, and its widest margin is the dorsal one. 

 This is shown by the position of the cloacal orifice with respect 

 to the foot, as seen in Fig. 6. Immediately behind the disk are 

 two minute lateral horn-like points, which project from the 

 head, and curve towards each other. These are sometimes 

 visible both in a frontal and a lateral view, and with the disk 

 closed or open (see Figs, a and b), but at other times the closest 

 scrutiny fails in discerning them (Fig. c) . Behind these, in the 

 median line, there is an organ which is never concealed : it is 

 the single antenna, which stands up perpendicularly from the 

 occiput to a great height (being almost half as long as the body, 

 exclusive of the foot), and generally arches over the front; but 

 is capable of vigorous and sudden movements to and fro, and 

 from side to side. It is evidently tubular throughout ; either a 

 simple tube with thick walls ; or else, if the walls are thin, 

 famished with a slender piston which runs through its length. 

 By analogy, this organ ought to carry a pencil of diverging 

 bristles at its extremity ; and Mr. Slack has so figured it ; and 

 has, moreover, mentioned in a private letter to me that he has 

 again detected these hairs of unwonted length. On the other 

 hand, I have utterly failed to detect the slightest trace of hairs 

 or of ciliary motion in the antenna of one which I watched most 

 carefully with powers of 600 and 800 diameters, aided by an 

 achromatic condenser; though the animal was in vigorous 

 condition, and threw about its tube most waywardly. I did 

 detect signs of what seemed to be both inspiration and ex- 

 piration through the tube ; for an atom of extraneous substance 

 that by accident was adhering to the tip, was now and then 

 suddenly drawn into the open mouth of the tube, and presently 

 as suddenly blown out. The appearance certainly favoured 

 Ehrenberg's notion of this organ being a respiratory tube. 



The disk when withdrawn forms a sort of pimple or mam- 

 millary prominence, with a pursed aperture, seated on the front 

 of the head. In this condition, and with this exception, the 

 general form of the trunk is cylindrical, with a slight, swell on 

 the dorsal aspect, and with the upper end rounded to the base 

 of the antenna, and the lower to a closely and strongly wrinkled 

 foot (Fig. a), of which, however, I have been able to see only 

 the extreme upper portion, at a moment of unwonted extension. 

 If, as is no doubt the fact, the lower extremity of the animal 

 was in contact with the surface on which the case was erected, 

 the foot must be capable of being drawn out to amazing length. 

 I do not doubt that such was the fact ; yet the upper portion of 

 the animal is certainly able to shift its aspect in the case, h,ad 

 that with a measure of persistency which appears rather to in- 

 dicate a voluntary change in the foot-hold than a mere twist. 



