2 I 2 ROTIFERA 



Ploima ; for though the majority of these present one or other of 

 the four varieties of the malleate type, Triartlira and Pterodina 

 (but not the other genera of their respective families) have the 

 gizzard malleoramate. 



The oesophagus is, when present, a contractile ciliated tube in 

 which the food makes no sojourn on its way to the stomach. 



The stomach may be nearly spherical, ovoid, or elongated and 

 cylindrical. Its walls are formed of large cells, often granular 

 and sometimes brownish, whence a hepatic function has been 

 assigned to them. Its apertures are both surrounded by con- 

 stricting muscular fibres. The intestine may be simple or 

 divided by a similar constriction into intestine proper and 

 rectum. The whole of the alimentary tract, with the exception 

 of the mastax, is richly ciliated within. The rectum opens into 

 the slender non-ciliated cloaca. The intestine is sharply bent 

 upwards and towards the back in the tubicolous forms, but is 

 nearly straight elsewhere ; in Trochosjihaera it is bent ventrally. 

 In Asplanchnaceae and in Paraseison there is no rectum, the 

 stomach being a blind sac. 



The so-called salivary glands, usually two in number, open 

 into the pharynx or mastax ; and the paired gastric glands (Fig. 

 106, (j(f) open into the oesophagus or stomach. While the pre- 

 hension of food is usually accomplished by the ciliary current 

 of the disc and pharynx, we have seen that a more active 

 swallowing action takes place in Flosculariaceae and Asplanch- 

 nidae, which devour whole Algae, Infusoria, and even other 

 Eotifers, the long spines of Triartlira not availing as a protec- 

 tion. Many Ploima put out the tips of their trophi to nibble 

 at debris, or, in the case of Diglena and Distemma, to attack 

 Desmids, or the Infusorian Stentor. But this use of the trophi 

 is most efficient in Plocsoma. Bilfinger 1 writes: "It has the 

 courage to attack larger Rotifers; thus I was able to observe 

 under the microscope how it fell upon a Eattuhis but little 

 smaller than itself and destroyed it. First it plunged the sharp 

 prongs of its mastax deep into the tender frontal area of its 

 unhappy victim; then followed a pumping action of the gizzard, 

 and stroke by stroke the whole contents of the victim's body 

 pa.ssed into the brigand's stomach." From this it is an easy 

 transition to the ectoparasitism of Drilophagus, Balatro, and 

 1 :! Zur Rotatoricn "Wurttemburgs, " in Jahrcsl. Vc,\ Wilrt. vol. 1. 1894, p. 57. 



