THE VICTORIAN NATURALIST. 113 



be abundant about our weed. It can readily be known by the 

 clear, bright, transparent lemon colour with which the trunk (not 

 the extremities) is tinged. Two bright red eyes are obvious, set 

 on its neck, as in all the Philodinas, and there is a prominent 

 dorsal antenna. Our engraving shows this Rotifer in what may 

 be called its sitting posture, the foot being partially closed up. 

 When it settles down thoroughly to work, it assumes this 

 attitude, and is then steady enough to satisfy the most 

 exacting observer. Another species of the same genus some- 

 times abundant appears to be the Large-wheeled Philodina, 

 P. megalotrocha. Its body is shorter, relatively plumper, and 

 slopes more gradually to the foot. The feature that strikes the 

 eye most at first sight, however, is the greater size of the wheels 

 when expanded. This quaint and pretty animal, smaller than 

 the last mentioned, but otherwise very similar (with the exception 

 of the colour), frequently behaves in a way that annoys the 

 observer. No sooner is its wreath unfolded than it detaches 

 itself and commences to swim away, so that we have to chase it 

 from place to place. 



The genus Rotifer is distinguished by the fact that the eyes 

 are situated on the frontal column, to which allusion has 

 already been made. A species of this genus that is frequently 

 present is the Common Rotifer, R. vulgaris. As the en- 

 graving shows, this is long and colourless, and much more 

 slender than the Philodinse. We find yet another species of the 

 same genus. It is as large and stout as a Philodina, and yellow 

 in colour. Added to these features its extraordinarily long foot 

 stamps it as being probably R. macrurus. One type of trophi is 

 universal in this second order. On account of its wide pre- 

 valence we have given a separate engraving of this, which is 

 called the ramate type (fig. 2). In observing a Rotifer of this 

 order, the beginner is sometimes puzzled to notice a second pair 

 of trophi (often in motion) towards the hinder part of the animal. 

 This mystery is explained by the fact that the eggs are hatched in 

 the mother's body, so that we see the unborn young, fully 

 developed. These Philodinadse possess a remarkable property, 

 which has given rise to an immense amount of heated con- 

 troversy during the last two centuries. When the water in which 

 they have been living dries up (provided the evaporation be not 

 too rapid), they roll themselves up into the form of a ball, coat 

 themselves with a gelatinous substance excreted by the skin, and 

 retire from active life till water is once more supplied. The 

 excretion, after hardening, protects the internal moisture of the 

 animal, which can survive in this condition many years. 



The third order of Rotifers comprises those which are essen- 

 tially swimmers. Ploima (sailing) is the name given to these. 

 They include the liveliest, most intelligent, and the most varied 



