178 ON SOME PECULIAR ORGANS OF THE INFUSORIA. 



high power, minute fusiform bodies may be detected thickly 

 imbedded in its walls, (Figs. 11 and 12 and 14 /i, Plate X.) 

 These bodies are perfectly colourless and transparent ; they 

 are about the l-2500th of an inch long, and may easily, even 

 without any manipulation, be witnessed at the margin, where 

 they are seen to be arranged perpendicularly to the outline 

 of the animalcule, while on the surface turned towards the 

 observer their extreme transparency and want of colour render 

 them invisible against the opaque back-ground, and it becomes 

 necessary to crush the animalcule beneath the covering-glass 

 so as to press out the green globules which it contains, in 

 order to bring the fusiform bodies into view. To these bodies 

 I propose to give the name of trichocysts. 



As long as the animalcule continues free from annoyance, 

 the trichocysts undergo no change, but when subjected to ex- 

 ternal irritation, as occurs during the drying away of the sur- 

 rounding water, or the application of acetic acid or other 

 chemical irritant, or the too forcible action of the compressor, 

 they become suddenly transformed into long filaments, which 

 are projected from all parts of the surface of the animalcule 

 (fig. 13); and it is these filaments which, being mistaken for 

 cilia by Cohn and Stein, gave rise to the erroneous views just 

 mentioned. 



The rapidity with which this remarkable change is effected, 

 joined with the great minuteness and transparency of the ob- 

 ject, renders it extremely difficult to follow it, and for a long 

 time I could only satisfy myself of the fact that the fusiform 

 bodies were suddenly replaced by the projected filaments. 

 After continued observation, however, I at last succeeded in 

 witnessing the principal steps in the evolution of the fila- 

 ment. 



It is not difficult, by rapidly crushing the animalcule, to 

 force out some of the trichocysts in an unchanged state. 

 (Fig. 15.) If the eye be now fixed (m one of the isolated tri- 

 chocysts, it will most probably be seen after the lapse of a 

 few seconds to become all at once changed with a peculiar 

 jerk, as if by the sudden release of some previous state of 

 tension, into a little spherical body. (Fig. 16.) In this con- 

 dition it will probably remain for two or three seconds longer, 

 and then a spiral filament will become rapidly evolved from 

 the sphere, apparently by the rupture of a membrane which 

 had previously confined it, the filament unrolling itself so 

 quickly that the eye can scarcely follow it (fig. 17), until it 

 ultimately lies straight and rigid on the field of the micro- 

 scope, looking like a very fine and long acicular crystal. 

 (Fig. 18.) 



