100 THE ROTIFERA. 



the form of little pink balls in the dried-up dirt of a house-gutter ; and whose revivifica- 

 tion he describes. It is very common in ponds, water-butts, and housetops ; and will 

 bear to be dried up and reanimated, again and again, without injury. It is, too, most 

 prolific in situations that suit it ; and these are sometimes odd enough. Lord S. G. 

 Osborne, for instance, found that the dust of two stone vases in his grounds at Blandford 

 was thick with the little pink spheres of P. roseola, and with the white ones of Adineta 

 vaga (Callidina vaga, Davis) ; and he supplied his microscopic friends for years with 

 this rotiferous dust. 



[The body is sometimes of a delicate flesh tint, often deepening to full rich red in the 

 cellular walls of the ample stomach, but fainter at the head and foot ; it is evident that 

 the tint does not depend on the nature of the Rotiferon's food, and it is quite as glowing 

 in the half- grown animal. 



The corona is large, with a deeply cleft sinus, and the two wheels of the ciliary 

 wreath are remarkably fine. The frontal column is large, cylindrical, truncate, and 

 strongly ciliated. The proboscis has a soft decurved hook on its very front (fig. 46), 

 which is probably a tactile organ of great sensibility. I believe that I have seen 

 it used for grasping the slender stems and filaments, laying hold of one between 

 the hook and the face. In progress through clear water the creature often makes a 

 perceptible snatch forward, as if it caught prey with the organ, though none was 

 visible. Only in accurate profile, and full extension can this be seen. The broad 

 head of the stomach embraces the base of the mastax ; and, when the animal is extended, 

 this viscus is so stretched that the middle portions are drawn thin, while the ends are 

 dilated. There is a short round distinct intestine ; and the cloaca is at the base of the 

 first joint of the foot. Two earlike triangular gastric glands are visible, one on either 

 side of the mastax ; and there is a small contractile vesicle which contracts about every 

 thirteen seconds : but the colour of the body and its longitudinal folds interfere greatly 

 with the sight of the internal organs. The eyes are of a beautiful pale red ; but are in- 

 visible by reflected light. Under pressure eight transverse muscles have been distinctly 

 seen, as shown in fig. 4rf. P.H.G.] 



Length. When extended, about $ ; in a dried condition they are globes of jj^ to 

 ^3 inch in diameter. Habitat. Ponds, water-butts, house-gutters : common. 



P. CITRINA, Ehrenberg. 

 (PL IX. fig 6.) 



Philodina citrina .... Ehrenberg, Die Infus. 1838, p. 501, Taf. Ixi. fig. 8. 

 Gosse, Tenby, 1856, p. 299, pi. xix. 



Pritchard, Infusoria, 1861, p. 705. 



. . . . Eckstein, Sieb. u. Koll. Zeils. Bd. xxxix. 1883, p. 353, 



Taf. xxiv. fig. 14. 



[SP. CH. Body smooth ivith a distinct constriction below the swelling disk, but no 

 collar; corona wide, with a deep square sidcus ; antenna nearly horizontal; eyes 

 minute, oblong, oblique ; teeth two ; foot moderately slender, abrupt. Transparent, 

 yellow. 



There is great resemblance of form between tliis and the preceding ; but the differ- 

 ences enumerated above, though mostly minute, help to distinguish it. The colour, 

 however, is the main peculiarity. This is normally a rich clear yellow, like a topaz ; 

 yet specimens occur in which the hue is much paler and duller : and the extremities are 

 always colourless. Under reflected light the creature is an object of great beauty. The 

 citron hue becomes positive, and brilliant, separated abruptly from the hyaline extrem- 

 ities ; while the whole animal assumes a sparkling, glittering appearance, reflecting the 

 rays of light from various points, as if it were carved out of a precious stone. 



Though there is no turgid neck, as in P. erythrophthalma, there is a more marked 

 constriction than in P. roseola, the hemisphere which carries the corona being more 



