THE INFUSORIA 



447 



organs, probably tactile, between the membranellaj of the adoral spiral of 

 Tintinmdce (Schweyer). 



The nature and mechanism of the peculiar trichocysts remains to be ex- 

 plained. The trichocyst in the unexploded state is a spindle-shaped body 

 with a fine, hair-like process at its outer end which reaches to the pellicle 

 (Fig. 186, D, T.). The exploded trichocyst tapers gradually to a sharp point 

 at its proximal end ; distally it shows a cap-like swelling (Fig. 187, D G). 

 According to Khainsky (170'5) the trichocyst consists of two portions : a distal 

 or outer part which stains deeply, and a proximal or inner part which stains 

 a lighter colour (Fig. 187, A C). 

 The unexploded trichocyst consists 

 entirely or almost entirely of the 

 darker substance ; in the process of 

 explosion the dark substance is con- 

 verted into the light, so that in the 

 exploded trichocyst only a small 

 portion of the dark substance 

 remains to form the distal cap. 

 The notion, recently upheld by 

 Mitrophanow (855), that the tricho- 

 cyst consists of viscid fluid con- 

 tained in a cavity in the ectoplasm, 

 whence it is expelled by a sudden 

 contraction of the ectoplasm, and 

 stiffens to a solid thread under the 

 action of the watery medium, 

 cannot be maintained (Schuberg, 

 44) ; nor does there seem to be 

 any ground for comparing it to a 

 Coelenterate nematocyst or to a 

 polar capsule of a Cnidosporidian 

 spore. According to Mitrophanow, 

 the substance of the trichocysts 

 appears first near the nucleus in 

 the endoplasrn as small grains which 



B 



FIG. 187. Trichocysts of Infusoria. 

 A E, Stages in the explosion of the 

 trichocysts of Paramecium caudatum, 

 showing the manner in which the tricho- 

 cyst grows in length, with conversion of 

 a darkly-staining substance into a lighter 

 material ; the fully-exploded trichocysts 

 are seen in D and E. After Khainsky 

 (170-5). F, G, Exploded trichocysts 

 of Frontonia leucas. After Schuberg, 

 magnified 1,500 diameters. 



C D E <3 



pass out into the ectoplasm. Tricho- 

 cysts do not occur in any Peritricha, 

 but in one species, Epistylis umbel- 

 laria, large oval nematocysts occur, 

 arranged in pairs a phenomenon 

 unique amongst the Ciliata. 



The contractile vacuoles open to 

 the exterior as a general rule, but 

 in the Peritricha, as already stated, 

 they open into the vestibule ; in 

 this order there is usuallj 7 a reservoir- 

 vacuole into which one or two con- 

 tractile vacuoles empty themselves, and which in its turn voids its 

 contents into the vestibule. In Campanctta, however, there is no reservoir- 

 vacuole,. and the single contractile vacuole opens by two canals into the 

 vestibule (Schroder, 804). In Opalina there are no contractile vacuoles, 

 and in some species (e.g., 0. ranarum) no excretory organs are to be found ; 

 but in other species the endoplasm contains an axial series of more or less 

 irregular vacuoles, opening one into the other and to the exterior by a poro at 

 the posterior end of the body. These vacuoles are sometimes in close relation 

 with the nuclei, often enveloping them to form a perinuclear space (Metcalf, 

 852). In Pycnothrix monocystoides the endoplasm is traversed by a branched 

 system of excretory canals, which unite into a single efferent duct opening at 

 the surface of the body near the posterior end by a pore ; the duct is ciliated. 

 and is homologized by Schubotz with the C3'topyge, which in Nyctotherus is 



