Basal granule. 

 Connectinq fibril . 

 Trlchocyst granule. 



Accessory 

 basal granule. 



.3 CILIATE PROTOZOA 



embedded peculiar structures known as trichocysts (Fig. 21). 

 These are spindle-shaped bodies with a fine point, and consist of 

 some semi-liquid substance. They are placed at right angles to 

 the surface, with the point in the outer part of the layer. If the 



animal be stimulated by 

 impact or by a solution of 

 some irritating substance, 

 they suddenly elongate and 

 project from the body as 

 threads, of which the points 

 are sticky while the rest has 

 hardened. The trichocysts 

 are organs of adhesion by 

 Fig. 22. — Paramecium which the animal anchors. 



multimicronucleatutn. ^-u -^ breaks free the 



Diagrammatic drawing of vvnen It oreaKS iree ine 



a portion of the dorsal threads are lost and the 



_,^ surface, showing a Hne of trichocysts replenished. The 



/ 4^\ hexagonal pits, the basal ,,. , ,^. s . i j 



"<!>>" granules, and the fibrils pelhcle (Fig. 22) IS marked 

 connecting them, x 3700. by rows of rectangular or 

 ~~ er un . hexagonal pits, in each of 



which a cilium arises, or sometimes a pair, while the trichocysts 

 lie under the transverse ridges between the pits. Each cilium 

 consists of a sheath surrounding a ring of nine double threads 

 and a central pair. Below the cilium a fibre is continued in- 

 wards into the cortex, within which it bears a swelling known as 

 the basal granule. The basal granules are united by a system of 

 threads known as neuronemes which are possibly conductile. The 

 endoplasm contains numerous granules, some of which appear to 

 consist of waste matter ready for excretion, while others may 

 be stored nutriment. Glycogen is diffused through the endoplasm. 



NUCLEI 



Paramecium caudatiim has two nuclei, one of which is large and 

 is known as the meganucleus, while the other, the micronucleus, 

 is small and is situated in a groove on the meganucleus. The 

 nuclei lie in the endoplasm above the gullet ; Paramecium aurelia 

 has two micronuclei. 



There are two contractile vacuoles, which lie in the cortex of 

 the dorsal side, one towards each end. At its full size each is a 

 large spherical space surrounded by from six to ten pear-shaped 



