370 



NATURAL HISTORY. 



flexible stem, which is for a while extended to the utmost, the cilia of the disc and peristome being 

 in full action. Suddenly the stem contracts, becomes spiral, and the body closes slightly and bends 

 on its stalk. Then the oral end opens, the cilia move again, and the stalk is drawn out to the 



utmost. This goes on very irregularly in a colony 

 of a score or more of individuals, so that whilst 

 some are contracted others are in full play. The 

 currents in the water, produced by the ciliary fringes, 

 are considerable and move much disintegrated 

 matter into the oral grooves. The phenomena of 

 fission and conjugation may be seen in the same 

 colony at the same time, and every now and then a 

 bud moves off by means of its hinder circle of cilia. 

 In the genus Carchesium, which belongs to 

 this group, a host of animalcules are on branchlets 

 springing from a common stem. Usually the bell- 

 shaped bodies are on one side of their branchlet, 

 and each one has a stem continuous with the branch 

 and main stem. A muscular tissue resembling 

 that of Vorticella is in the stem and its prolonga- 

 tions, but it is discontinuous, so that each body can 

 contract without the others, and each branchlet 

 can do the same irrespectively of others, and the 

 whole may contract with the primary stem and 

 form a small globular mulberry -looking mass. 



The species live in fresh and sometimes in 

 salt water, and the whole colony originates in the 

 fission of one individual and its stalk, and is fully 

 developed by the successive longitudinal fissions of 

 body after body (Fig. 28, D). 



The semis Zoothamnium has the animalcules 



Fig. 28. A, ZOOTKAMXIt'M XIVEUM (SnviUe Kent) ', B, 

 SINGLE ANIMALCVLE, MOKE HIGHLY MAGNIFIED ; C, 



EPISTYLIS UMBILICATA; r>, BRANCHLET OF CARCHESIUM 



POLYPINUM ; E, AX EPISTYLIS GROWING ON A CYCLOPS. 



like those of Vorticella, but often dissimilar in 

 shape and of two sizes, and they are placed at the 

 end of a branching, highly contractile stem. The 

 internal muscle of the stem is continuous throughout. This is not spiral in its construction, so that 

 the stem never forms a spiral during its contraction. In Zoothamnium niveum, 

 which is a salt-water form, there are spherical animalcules of large size near the 

 bases of the primary branches, and the smaller ones at the ends of branchlets are 

 long bell-shaped (Fig. 28, A, B). 



Another genus, Epistylis, with its animalcules closely resembling Vorticella, 

 has them attached in numbers to a rigid, uncontractible, 

 branching, tree-like stem, and the bodies are of the same 

 size throughout. Epistylis fiavicans forms slimy encrusta- 

 tions on water plants and on the sides of aquaria. Many 

 species settle on small Crustacea (Fig. 28, c, E). 



The next sub-family includes animalcules which excrete 

 hard sheaths as loricre and live within them. The genus 

 Pyxicola, whose species live for the most part in salt water, 

 has an erect lorica or a stem of attachment, and a horny 

 plate on the body beneath the border of the peristome. 

 This closes in the top of the lorica when the animal retreats. 

 They inhabit fresh and brackish water (Fig. 29). 

 The last sub-family, the Ophrydiiire, contains Vorticella-like animalcules which excrete and 

 inhabit a soft mucilaginous sheath or mass which may contain many. 



Fig. 30. OPHEYDIUM EICH 



HOENII. (After Saville Kent.) 

 a, 0. sessile, natural siz?. 



Fig. 29.^1 



PYXIDIFOEMIS. 



