25S The Unity of the Organism 



which they can be observed it has naturally come about 

 that they have been studied most and are the most accu- 

 rately known of all the organs of these small animals. But 

 extensive researches in recent years have brought to light 

 a whole system of organs in one group of protozoans, the 

 flagellata, that was entirely unknown a generation ago. The 

 subdivision of the flagellata referred to contains the try- 

 panosomes, animals which have come into prominence lately 

 because many of them are parasitic in man and beast, pro- 



-Tf-UC. 



FIGURE 8. CRITHIDIA LEPTOCORIDIS ( AFTER McCULLOCh). 



a.f., axial filament, bas.gr., basal granule, c, centrosome. rh., 

 rhizoplast. nuc, nucleus. 



ducing a long list of diseases of which sleeping sickness is 

 probably the most generally known. As we are now more 

 interested in the organisms than in the effects they have upon 

 their hosts, other species akin to the trypanosomes, but un- 

 known except among specialists, will best sei*ve our purpose. 

 The examples I select are shown in figures 7 and 8. The 

 species illustrated by figure 7 is Crithidia leptocoridis 

 McCulloch.* This species has been chosen for the purpose 

 of showing the newly discovered system of organs mentioned 

 above, so structural details other tlian those of the system 

 are not shown in the drawing. 



* This occurs in various parts of the United States. The descrip- 

 tion of the creature is by Miss Irene McCulloch (An Outline of the 

 Morphology and Life History of Crithidia lepiororidis, n. sp. Univ. of 

 Calif. Pul)l. /ool., \'ol. Hi, pp. 1-22, 191.5), one of the group of students 

 in protozoology working under the guidance of Professor Kofoid, 



