282 University of California Publication* in Zoology [VOL. 20 



ENDOPLASMIC STRUCTURES 



Endoplasm. Within the ectoplasm the body is composed of the 

 endoplasm (end., pi. 27, figs. 7 and 8; pi. 28, figs. 9 to 12) and the 

 inclusions therein. The endoplasm is less dense than the ectoplasm 

 and more coarsely granular. It is quite fluid, having a fairly definite 

 circulation in the active organism. From the inner end of the 

 oesophagus the direction of flow is posteriorly along the ventral sur- 

 face dorsalward just before reaching the posterior end, thence an- 

 teriorly along the dorsal surface. Just as it reaches the ectoplasm 

 of the apical cone, it is deflected posteriorly down through the central 

 portion of the body dorsal to the rootlets of the adoral cilia. This 

 course can be followed readily by observing the circulation of the food 

 vacuoles. 



The food vacuoles are customarily globular and may contain starch 

 granules, bacteria, or indigestible particles, of the food of the host. 

 The ingestion of bacteria is probably abnormal since it seldom occurs 

 except when the number of bacteria in the medium has increased 

 greatly during incubation. The starch granules may occur in enor- 

 mous numbers especially when the host has recently been fed on grain. 

 Red blood cells have not been noted in any of the balantidia observed 

 during the work. 



That Balantidium may be cannibalistic is the only possible in- 

 terpretation of several findings. In these instances small individuals 

 were lying within the endoplasm of extremely large individuals 

 (100 X 125/i) and were in a state of disintegration. The larger indi- 

 viduals were Balantidium coli in every case and the smaller may have 

 been Balantidium suis, for both species were present in the material ; 

 but disintegration of the latter had progressed so far that specific 

 identification was uncertain. The possibility of interpreting this 

 phenomena as sporulation, which was described by Walker (1909), 

 is precluded by the disintegration of the included organism and the 

 fact that the normal vegetative phase of the nuclei of the large indi- 

 vidual is unmodified. Further evidence is to be found in the fact 

 that never more than a single individual has been found inside 

 another, while sporulation would produce several. 



Macronucleus. As is generally the case in ciliates, balantidia are 

 binucleate, having a large macronucleus and a small micronucleus. 

 The macronuclei of Balantidium coli and Balantidium suis are slightly 



