722 



PROTOZOA. 



reason, in a state of disturbance, the minute gelatinous balls lie hidden close 

 to the surface of some water weed at the ends of their tightly coiled stalks, 

 and thus easily elude observation. But if the water is at rest, the observer, 

 through the microscope, will see them gradually emerge from their place of 

 refuge, one individual after another rising into view on its slowly uncoiling 

 stalk, the ball lengthening and assuming the shape of a bell about ^\^ of an 

 inch in length. Long cilia, fringing a spiral membrane which can be pro- 

 truded beyond the aperture of the bell, wave about in the water, and bring 

 within reach particles of food that are swept down a groove leading to the 

 inner protoplasm. As such a group of Bell animalcules is watched, one 

 individual or another suddenly vanishes, being drawn down instantaneous^ 

 by the contraction of its stalk, while others more gradually come into sight. 

 These animalcules multiply by dividing lengthwise ; the young form, when 

 provided with its circle of cilia, breaks loose from the parent and swims 

 about freely for a time before attaching itself by a stalk. Young are some- 

 times also produced within the parent as spores. 



These beautiful creatures are often found in colonies of various shapes, 

 some of the most delicate (Fig. 10, A) resembling the frond of a maidenhair 



fern. The stem is, in such cases, formed 

 of protoplasm, produced by the various 

 individuals of the colony, which are not 

 always all alike. In the form illustrated 

 spherical individuals without stalks are to 

 be seen attached at the bases of the 

 branchlets which carry the other in- 

 dividuals. 



In the fourth division of the Ciliated 

 Infusorians the cilia are confined to the 

 lower surface of the body, and are some- 

 times changed into bristles or hooks ; these 

 forms are much less attractive in appear- 

 ance than those we have just described. 



We come, in the last place, to the 

 Tentacled Infusorians which are often to 

 be found attached to pond weeds by long, 

 straight stalks. The soft body is usually 

 contained in a cup-like sheath, sometimes 

 triangular in form, and terminates at the 

 free end in one or more projecting knobs, 

 ornamented with groups of stiff, hollow 

 tentacles. The animal has no mouth, but 

 feeds by means of these tentacles, the minute discs in which they end 

 arresting and piercing the bodies of any small animalcules that come 

 within reach. The soft parts of the victim are sucked up through the 

 hollow tentacles and drawn into the body within the. sheath. These 

 stationary bodies give rise, by means of budding, to free young forms with 

 cilia which swim about for a time, then attach themselves, lose their cilia, 

 and develop tentacles like those of the parent form. 



These Tentacled Infusorians sometimes form very complicated colonies 

 consisting of creeping roots, from which rise trunks and branches (Fig. 10, B). 

 Each branch and branchlet terminates in an individual with its radiating 

 tentacles, bub besides these tentacled members of the colony there are other 



Fig. 10 TNFUSORIAV COLONIES. 



A, Zoothamnium. 



B, Dendrosoma. 



