PHYLUM PROTOZOA 



75 



the normal shape and structure (although the trichocysts are often discharged), 

 but finally they round up and become abnormal. When this happens find 

 another specimen. This method is very successful, provided that the proper 

 concentration of formaldehyde is used. 



All observations with the high power must be made with a cover glass over 

 the material. Do not allow the material to dry up. Make observations only 

 upon normal specimens, as far as practicable. With a little patience all of the 

 following details of structure can be observed. 



Paramecium, like Amoeba, consists of but a single cell, but whereas the latter 

 is a mass of nearly homogeneous protoplasm, showing little differentiation, the 

 protoplasm of Paramecium has become differentiated into a considerable number 

 of different parts, as the following description will demonstrate. 



a) Ectosarc: The outer layer of protoplasm of the Paramecium is called the 

 ectoplasm or ectosarc. The surface of the ectosarc is differentiated as a firm 

 membrane, the cuticle or pellicle, to which the animal owes its permanent shape. 

 It is marked with a mosaic of hexagons which is not usually demonstrable (see 

 Hegner, Fig. 24, p. 62). From all over the cuticle arise delicate threadlike 

 processes of the protoplasm, the cilia, whose co-ordinated movement like numer- 

 ous little oars propels the animal through the water. The cilia are practically 

 of the same length over the body except that there is a tuft of longer ones on the 

 posterior extremity. Those in the oral groove are especially active. The cilia 

 are best seen by focusing on the edge of the animal. The layer of ectoplasm 

 under the cuticle contains innumerable rodlike bodies lying parallel to each 

 other and at right angles to the surface. They are best seen by focusing on the 

 edge of the animal, as in the central parts 01 the animal they are viewed from 

 the end and hence appear as dots. They are called trichocysts and appear to be 

 little oval sacs containing a viscous fluid. Upon stimulation this fluid is dis- 

 charged through the minute opening of the trichocyst and hence is squeezed 

 out into the form of a long thread. Enter the layer of trichocysts and the cilia 

 upon your outline drawing. Do not make a new drawing. 



b) Endosarc: The central mass of the Paramecium is the endoplasm or 

 endosarc. It is much more fluid than the ectosarc and is filled with granules. 

 It generally contains a number of spherical vacuoles packed with food particles, 

 designated as food vacuoles. It contains the nuclei (see below). Enter details 

 of the endoplasm on your drawing. 



c) Digestive apparatus: This is best studied on a normal active animal, one 

 that is resting quietly near some object. It can also be seen on formalized 

 animals but not on those which have been flattened out by withdrawal of water. 

 Having found a favorable individual, watch the posterior end of the oral groove 

 (be sure you know where this is) for an oval clear spot. This is the so-called 

 mouth. Then observe a clear funnel-shaped curved cavity leading posteriorly 

 from the mouth down into the endoplasm. This is the gullet or cytopharynx. 



