724 THE AMERICAN NATURALIST. [Vol. XXXIX. 



developed entirely out of the cytoplasmic network. The au- 

 thors are unable to distinguish a kinoplasm distinct from the 

 general network of the cell. These are vital points of differ- 

 ence which are fundamental to the understanding of mitotic 

 phenomena and rest of course on matters of fact. The chief 

 points at issue concern the structure and development of the 

 asters and the nature of the material at their centers. My own 

 studies and those of Farmer and Chamberlain have convinced 

 me that there is an accumulation of substance (kinoplasm) in 

 the centers of the asters and polar caps to such an amount that 

 it must be regarded as a definite structure in the cell and its 

 morphology and relations to the spindle have certainly justified 

 us in considering it as similar to the centrosphere of the thallo- 

 phytes. 



4. The Essential Structures in the Plaistt Cell and 

 THEIR Behavior in' Ontogeny. 



The cell is composed of a series of osmotic membranes be- 

 tween which are included a number of protoplasmic structures 

 whose morphology and minute organization is various. They 

 are : the outer plasma, the vacuolar, and the nuclear membranes. 

 Each of these sustains a relation to some fluid which bathes its 

 surface. The fluid nature of the nuclear sap and cell sap is 

 obvious but the outer plasma membrane is also against a moist 

 surface since the cell walls of tissues are normally saturated with 

 water. The structure of the plasma membranes is apparently 

 the same. They consist of the homogeneous finely gran- 

 ular protoplasm that is designated kinoplasm. The protoplas- 

 mic structures included within the plasma membranes may be 

 grouped as cytoplasmic and nuclear. The greater part of the 

 cytoplasm, including that which is termed trophoplasm, has an 

 organization peculiar to itself and very different from that of 

 the plasma membranes. This structure has been described as 

 alveolar or of the nature of foam and sometimes fibrillar and 

 with various large granular inclusions. The cytoplasm also con- 

 tains the characteristic organs termed plastids. The conspicu- 

 ous structures of the nucleus are : the chromatic elements 



