NUCLEI AND KINETIC ELEMENTS 



83 



definite body, the substance of which forms the pole plates. Hertwig 

 (1898) and Doflein (1916) assume that they are formed from the 

 linin substance of the nucleus. On this assumption the pole plates 

 might be interpreted as hyaline aggregates of the linin reticulum of 

 the nucleus, indeerl, the hyaline and homogeneous appearance of 

 the pole plates is suggestive of amoeba ectoplasm. ^Yith our present 

 knowledge I am inclined to agree with this interpretation of pole 

 plates and to regard Paramecium caudatum, with other species of 

 this genus, Actinosphcpriiim eichhornii and the other forms men- 

 tioned above, as containing no intranuclear kinetic elements. To 

 such a group we would also assign forms like Aulocantha scolymantha 

 and Chilomonas paramecivm, in which according to observations of 



Fig. 40. — Micronucleus of Paramecium caudatum in the prophases of the first 

 meiotic divi.sion. A, Early stage in the formation of chromosomes; B, elongation 

 of the nucleus prior to crescent formation ; C, metaphase of the first division. Dehorne 

 describes the entire chromatin aggregate as forming one highly convoluted chromo- 

 some. (After Dehorne.) 



Borgert (1909) and Alexeieff (1911), not only intranuclear kinetic 

 elements but pole plates as well are entirely absent. 



(6) Extranuclear (Cytoplasmic) Kinetic Elements.— It is in the 

 cytoplasm that kinetic elements are most highly differentiated, and 

 the often perplexing structures which appear in different types of 

 Protozoa have led to much confusion in terminology. Any attempt, 

 therefore, to present a clear picture of the diverse elements and to 

 distinguish one type from another, inevitably leads to contradictions 

 in connection with interpretations of one or another observer. 

 The facts may be marshalled, however, into a fairly logical and con- 

 sistent series indicating an increasing complexity in the organization 

 of the cell. Such a series is presented in the following pages with 



