68 BIOLOGY OF THE PROTOZOA 



tioned above, as containing no permanent intranuclear kinetic 

 elements. To such a group we would also assign forms like Aulo- 

 cantha scolymantha and Chilomonas paramedian, in which according 

 to observations of Borgert (1909) and Alexeieff (1911), not only 

 intranuclear kinetic elements but pole plates as well are entirely 

 absent. 



On the whole I would interpret the intranuclear kinetic elements 

 of Protozoa as originating by condensation of the ground substance 

 or karyolymph of the nucleus. In Paramecium caudatum (Figs. 35, 

 147) both in vegetative and meiotic divisions, the ground substance 

 forming the pole plates shows but little condensation (Fig. 57), 

 but in the first meiotic division of Uroleptus halseyi the karyolymph 

 forms two irregular masses which condense to form the spindle 

 fibers and the two spindle poles which are more like pole plates 

 than like centrioles (Figs. 151, 153). In a similar stage of Uroleptus 

 mobilis, however, condensation results in the formation of a definite 

 centriole which divides with a connecting centrodesmose (Fig. 32). 

 In the flagellate type the endobasal body may well be a permanent 

 condition of such condensation. Whether or not such condensations 

 leading to endobasal body formation involve a specific chemical 

 make up, different from that of the karyolymph and from chroma- 

 tin, is an unsolved problem. The diffuse forms such as may be seen 

 in pole plates do not stain with iron hematoxylin or other nuclear 

 dyes nor do they give a positive Feulgen reaction. The centrioles 

 and permanent endobasal bodies stain with iron hematoxylin but 

 the Feulgen reaction is negative. 



II. CYTOPLASMIC ELEMENTS OF THE FUNDAMENTAL 

 ORGANIZATION. 



Very little work has been done on the finer structures of encysted 

 Protozoa, and we are relatively ignorant of the make-up of the 

 fundamental organization of the cytoplasm. It is difficult, and 

 often impossible, to distinguish between those elements which are 

 essential parts of the germinal protoplasm and those which are 

 formed as a result of metabolic activities. The latter, obviously, 

 would belong to the structures of the derived organization. 



The great majority of the structural elements of the cytoplasm 

 are known only in the adult organism. Many of these are undoubt- 

 edly derived structures of the developing individual but some may 

 be essential parts of the germinal protoplasm. Until further knowl- 

 edge of the origin of such questionable elements is available we 

 may regard them tentatively as parts of the fundamental organiza- 

 tion and describe them as such. In most cases they are present in 

 the adult organism in the form of granules which, morphologically, 

 are almost indistinguishable from one another but which react 



