356 EDWIN G. CONKLIN 



ing cells. It serves to hold the fully formed mitotic spindle in a 

 definite position with respect to the cell surface; in early pro- 

 phases and in resting stages these connections are relaxed so that 

 spindles or nuclei may be moved out of their normal positions, 

 but these connections are not easily destroyed and they always 

 hold the nuclei and centrospheres in the same relative position 

 to the cell surface, however much they may be stretched. 



2. The structure of protoplasm 



The identification of a more viscid and a more fluid portion of 

 the protoplasm in centrifuged eggs leads to a consideration of the 

 relation of these two constituents of protoplasm to each other 

 and to various cell inclusions; it also raises the question of their 

 relation to the polarity and orientation of development. 



It has long been evident that protoplasm is not a homogenous 

 fluid. Dujardin held that 'sarcode' was a ''substance gluti- 

 neuse, parfaitment homogene, elastique, contractile, diaphane. 

 . . . . On n'y distingue absolument aucune trace d'organi- 

 zation, ni fibres, ni membranes, ni apparence de cellulosite." 

 (Quoted from Henneguy 'La Cellule,' p. 31.) Max Schultze, 

 Haeckel, Kiihne and many other early observers regarded proto- 

 plasm as a fluid owing to phenomena of protoplasmic flowing 

 and of surface tension. Brticke ('61) first contested the possi- 

 bility of this on a priori grounds, holding that a homogeneous 

 fluid would be unable to perform the functions which proto- 

 plasm performs, and maintaining that it must have a 'special 

 structure' or 'organization' made up of more liquid or more 

 solid parts among which are the 'smallest living parts' or vital 

 units. All students of protoplasm now agree that it is composed 

 of more fluid and more solid parts, though there is much differ- 

 ence of opinion as to the form of each of these and their rela- 

 tion to each other, as is shown by the various theories on the 

 'structure of protoplasm.' Different names have been given by 

 authors to the more fluid and the more solid parts of protoplasm 

 as indicated in the following incomplete list : 



