ORDERS OF ROTIFERA 791 



2. BDELLOIDA (the leech-like). That swim with their ciliary 

 \vivath, and creep like a leech. 



3. PLOIMA (the sea-worthy). That only swim with their ciliary 

 wreath. 



4. SCIRTOPODA (the skippers). That swim with their ciliary wreath 

 and skip with arthropodous limbs. 



The order Rhizota contains two families, chiefly differing from 

 each other in the position of the mouth, which in the FloaculariidcK 

 (figs, l and 2, Plate XVII) is central, lying in the body's longer axis, 

 but in the Melicertidce (fig. 3, Plat^e XVII) is lateral. Almost all the 

 species of both families live in gelatinous tubes secreted by themselves, 

 and often fortified in various ways : by debris gathered from the 

 water by the action of their ciliary wreaths and showered down at 

 random ; by pellets formed in a ciliated cup near the anterior end 

 of the body, and deposited in regular order on the gela- 

 tinous tube ; or by large ftecal pellets also regularly 

 deposited. 



The second order, JBdeUoida (fig. 7, Plate XVII), while 

 having many points in common with the Melicertidce,, have 

 a foot peculiarly their own. It has several false joints FIG - 6 5- 

 that can be drawn one within the other like those of a jmJ/nna 

 telescope. The corona consists of two nearly circular discs, i n tube, 

 a ch surrounded with a double row of cilia, and both of 

 these can be withdrawn into an infolding of the ventral surface at the 

 anterior end of the body, leaving the animal with a long pointed 

 conical head. When the discs are so furled the animal fixes the toes of 

 its foot, elongates the foot and body, catches hold with the furthest 

 point of the conical head, releases the foot, and then, contracting the 

 body and foot while the head remains fixed, draws forward the toes 

 and refixes them, and so da, capo. It can swim, however, in the usual 

 fashion, with its ciliary wreath. All the species of this order can, 

 under proper circumstances, be dried up into balls, which will retain 

 their vitality for even years, though in a state of utter dustiness. 

 This is due to their secreting round their bodies (after having drawn in 

 both head and foot) a gelatinous covering which retains the body-fluids 

 safe from evaporation. 1 This process takes some time, so that if 

 MII attempt is made to dry them on an ordinary glass-slip they simply 

 disintegrate. In a house gutter or in wet moss or sand, where the 

 drying up of the water, in which the Rotifera are, is slowly accom- 

 plished, the animals have time to complete their gelatinous coverings 

 before the water fails them. In this order the males have not as yet 

 been discovered. 



The third order, Plo'ima, is divided into a loricate and an illoricate 

 group, which are not, however, very sharply separated ; as in some 

 cases the outer layer of the skirf is, though horny, yet thin and 

 flexible. Brachionus rabetis (fig. 601), which has already been fully 

 described, is a good type of the Loricata find Copeus cerberus (fig. 6, 

 Plate XVII) of the Illoricata. Most of the species of this order have 



1 See Davis in Monthly Microsc. Journ. vol. ix. 1863, p. 207; Slack, at p. 241 of 

 same volume ; and the report of a discussion on the subject at the Royal Microsco- 

 pical Society, Jo urn. of Itoi/al Microsc. Soc. 1887, p. 179. 



