G4 LABORATORY STUDIES IN ZOOLOGY 



The most striking structural feature to be noted in the swim- 

 ming Paramecium is the depression or broad curved groove which 

 interrupts the even surface of the foremost end. This concavity, 

 the oral groove, extends diagonally from the tip of the foremost 

 end to a point beyond the middle of the body, where it terminates 

 in the "mouth." Study the relative widths of this groove and 

 the body at different places, compare the length of the organism 

 with its width, and determine the angle of slant of the oral groove 

 when the oral surface (that in which the mouth is located) is 

 toward the observer. 



Make an outline drawing about five inches long of that aspect 

 of the animal in which the oral surface is toward the observer. 

 Only the general form of the body and the oral groove need be 

 shown, but as details of structure will be added later special 

 care should be used in representing proportions. 



Various methods have been employed to decrease the rapidity 

 of movement of both animal and its cilia, thereby facilitating 

 the study of details. Before trying any of these, however, look 

 for animals near a piece of scum or other foreign materials which 

 are usually abundant in the cultures. Paramecia usually remain 

 relatively quiet around such material and are studied most 

 satisfactorily when in a normal state. Failing in this ask your 

 instructor for suggestions as to methods of slowing down the 

 activities of these animals. 



Compare the degree of differentiation of structures to be found 

 in Paramecium, when studied under high power, with that 

 observed in amoeba, as suggested in the outlines which follow. 



The cytoplasm of Paramecium comprises two regions, ecto- 

 plasm and endoplasm. The stratified ectoplasm is rather 

 highly differentiated. The outer layer, or cuticle, is a firm mem- 

 brane to which the animal owes its permanent shape. Study a 

 demonstration preparation of an animal in which the trichocysts 

 have been discharged following stimulation with weak picric 

 acid. Long threads of the discharged contents of the tricho- 

 cysts can be seen surrounding the animal. How does their 

 length compare with that of the cilia? These structures are 

 supposed to be both offensive and defensive in nature. The 

 innermost or cortical layer of the ectoplasm contains the main 

 portion of the trichocysts as well as the two pulsating contractile 

 vacuoles. These, aside from eliminating water, possibly aid the 

 animals in maintaining their balance. The two vacuoles appear 



