ROTIFERA. 633 



trochus ventrally. The latter is sometimes lobed or broken up into isolated 

 eminences. The cingulum forms five long processes fringed with stout 

 cilia in Stephanoceros, or five knobs each with a bundle of long cilia, usually 

 motionless, in Floscularia. 



The foot is sometimes absent, e. g. Asplanchna. It may be short or 

 long ; sometimes transversely wrinkled, e. g. Pterodina, or segmented ; it 

 terminates with two styles, or in a disc, as in tubicolous forms and occasionally 

 in free, e. g. Pterodina. It is in the latter case surrounded by cilia, as it 

 is in tubicolous forms before they become attached. The coelome does not 

 extend into it, but it contains two glands, the secretion of which serves for 

 attachment. 



There are muscles for the retraction and extension of both the trochal 

 apparatus and the foot, disposed partly in a circular, partly in a longi- 

 tudinal direction. They are colourless and sometimes striated. The jaw 

 apparatus and the digestive tract have their special musculature. Connective 

 tissue cells with fine processes unite the various organs which lie in a well- 

 developed coelome. The latter is probably to be considered an archicoele. 

 The blood (haemo-lymph) is clear, as a rule colourless, and often contains 

 granules but no corpuscles. 



There is a single dorsal ly placed nerve-ganglion composed of round 

 cells. It lies above the pharynx and gives off nerves anteriorly as well 

 as to the dorsal sensory organ or antenna (calcar). The latter is repre- 

 sented by a bundle of sensory hairs, sometimes borne upon a peduncle, 

 and it may be double or probably divided. In many Rotifera there is a 

 pair of similar but laterally placed organs, somewhat posterior in position, 

 but not supplied directly from the ganglion. An unpaired or paired eye 

 generally lies behind, upon, or in front of the ganglion. It consists of 

 a reddish pigment, in which a clear lens is found imbedded in some species. 

 Many Rotifers possess a remarkable globular or kidney-shaped mass of 

 calcareous granules in connection with the ganglion, the significance of 

 which is unknown. 



The mouth is anterior, nearly terminal in tubicolous forms, but more 

 or less ventral in others. The digestive tract is usually ciliated throughout. 

 The mouth leads into an oesophagus, followed in Flosculariadae by a crop, 

 but usually directly by a muscular pharynx or mastax containing the 

 chitinous jaw-apparatus or ' trophi.' These consist of two hammer-like 

 bodies, the mallei, which work against an incus or anvil. Each malleus 

 consists of a manubrium jointed to an uncus ; the incus of two pieces, rami, 

 borne upon a single piece, the fulcrum. The shape of the ' trophi' is 

 variable. The stomach is globular or cylindrical, and receives the secretion 

 of two glands placed at its commencement and in some of a large simple 

 or lobed glandular mass as well. The intestine is pyriform and opens 

 into a rectum or cloaca, which also receives the duct of the nephridi and 



