206 NATURAL HISTORY OF BHOMPSTON POND. 



with which these tiny processes are moved affords an 

 astonishing sight. The somewhat oval carapace which 

 extends beyond the limits of the body is raised in the 

 centre, and in some species is delicately striated by fine 

 longitudinal ridges, in others, by rows of tiny excrescences. 

 In some species again, four setae project from the posterior 

 margin of the carapace. When examined under a medium 

 power their characteristic movements can easily be observed. 

 They mostly crawl about the debris, and only reluctantly, as 

 it seems to us, will they leave this security and venture 

 forth into the open water, such a departure usually leading 

 to a sudden return by a series of irregular darts. 



Passing now to those forms whose bodies bear at least one 

 spiral of cilia, but are otherwise unciliated (Peritricha), one is 

 struck with the beauty and profusion of the commonest type, 

 Vorticella (fig. 14, 15). Even when its movements are 

 magnified several hundred times, its activity no less deceives 

 one's eye than its sensibility surpasses one's understanding. 

 Vorticella is attached to objects by a long delicate stalk (a), 

 the axial part (b) of which acts as a muscle fibre, which, upon 

 stimulation, rapidly draws the body towards the point of 

 attachment, the stalk becoming spirally coiled (c), and the 

 body spherically contracted (d). The slow return to the 

 expanded condition is due to the elasticity of the cuticular 

 covering. The campanulate body terminates in the peristome 

 (e) enclosing the disk (f ) and the groove in which the cilia are 

 situated (g). When the animal is irritated, besides the stalk 

 contracting \vithin the cuticular sheath, the peristomial lip 

 and the disk are approximated, the cilia thus becoming 

 efficiently protected in a temporary tube. If Indian ink is 

 irrigated, the vortex produced by the ciliary movements is 

 very obvious, and the minute particles can be watched 

 collecting in the pharynx (h) which leads through the cortical 

 layer and cuticle to open into the groove where the disk is 

 most elevated. The ink in the food vacuoles (i) may be 

 observed to course through the protoplasm, and to be finally 

 ejected at a definite point into the groove. There is a 



