GENERAL MORPHOLOGY 29 



The trophonuclei also may be permanently distribnted in the form 

 of chromatin granules, or, under certain conditions of the environ- 

 ment, may assume this condition (chromidia formation). The former 

 is characteristic of the vegetative nucleus of some infusoria (e. g., 

 dileptus. Fig. 2), the latter as a result of starvation or overfeeding, 

 or other abnormal environmental condition (e. cj., "chromidia" 

 formation in actinospherium, Hertwig). (For further discussion of the 

 significance of chromidia formation, see page 115.) 



In addition to the chromatin elements which enter into the make-up 

 of nuclei, there are specific materials of the cell which apparently 

 underlie the kinetic functions of protozoa. In some cases these are 

 aggregated into definite nucleus-like bodies to which the name kineto- 

 nucleus (Woodcock) has been applied (e. g., in trypanosoma and 

 other flagellates). Such organs of the cell will be considered at greater 

 length in the following section. 



(/') Kinoplasm. — The cjuestion as to a specific motor or kinetic 

 substance in the cell has been repeatedly raised in general cytology 

 and is still unsettled. Strasburger has long maintained that the plant 

 cell possesses such a specific kinetic substance, which he termed 

 "kinoplasm" and which enters into the formation of mitotic figures, 

 flagella, cilia, and the peripheral zone of protoplasm. It is, according 

 to him, a substance which forms all of the motor organs and underlies 

 all of the physical activities of the cell. Similarly for animal cells, 

 Boveri ('88) early pointed out that the astrospheres and other parts 

 of the spindle figure are composed of a substance apparently quite 

 different from the rest of the protoplasm, and suggested the term 

 "archoplasm" for it. Subsequent observers have amplified this view 

 and some, notably Prenant, have endeavored to show that archo- 

 plasm, or, in a larger sense, kinoplasm, is not only specific, but a kind 

 of "superior" protoplasm, self-perpetuating and distinct. Wilson 

 ('00), summing up the evidence for and against such a view in relation 

 to metazoan cells, comes to the conclusion that such substances, if they 

 exist in the cell, represent a more or less persistent but not permanent 

 phase, or product, of cellular metabolism. {The Cell, page 323.) 



Prenant's point of view is probably the most satisfactory in con- 

 nection with the protozoan cell, for here the specific substances are 

 more persistent than in the higher animal cells, and in most cases they 

 assume the form of definite, active, kinetic bodies closely associated 

 with the mechanism of nuclear division and of locomotion. To this 

 body of the protozoan cell, whether within or without the nucleus, 

 the non-committal term "division centre" has been applied (Calkins, 

 1898). 



In many different kinds of protozoa this division centre remains 

 inside the nucleus, giving rise to what Boveri has called the "centro- 

 nucleus" type. It is almost universally found among the represen- 



