6o 



AN INTRODUCTION TO ZOOLOGY 



outside of the ectosarc. 

 Lying in the ectoplasm 

 are a great number of 

 minute sacs, the trichocysts 

 (tr.) } which discharge long 

 threads to the exterior 

 when properly stimulated. 

 One large contractile vacuole 

 is situated near either end 

 of the body, close to the 

 dorsal surface, while a 

 variable number of food 

 vacuoles (/..) may usually 

 be seen. The nuclei are 

 two in number, a large 

 macronucleus (ma.) and a 

 smaller micronucleus (mi.) ; 

 these are suspended in the 

 ectoplasm near the mouth 

 opening. The anal spot 

 (an.) can be observed only 

 when solid particles are dis- 

 charged. It is situated 

 just behind the posterior 

 end of the oral groove. 

 FIG. 23. Paramecium viewed from the oral Detailed Anatomy. 

 surface. L, left side; R, right side. ,, , L , /T ,. 



The endo plasm (rig. 23, 

 an., anus ; cc., ectosarc ; en., endo- r ^ 



sarc; f.v., food vacuoles; g., gullet; en -) of Paramecium occu- 

 m., mouth ; ma., macronucleus ; mi., pies the central part of 

 micronucleus ; o.g., oral groove ; p., the body. It is supposed 

 pellicle; /r., trichocyst layer. The to be alveolar in structure, 

 arrows show the direction of move- , , < .. i i i 



, , , , Most of the larger granules 



ment of the food vacuoles. (From e . & . 



Jennings.) contained within it are 



shown by microchemical 

 reactions to be reserve food particles; they flow from place to 



