THE ECTOPLASM 



time the early stages of normal differentiation, unaccom- 

 panied, however, by growth, i.e., increase in length. 



. . . The movement of the embryonic cells in the lymph 

 clot is very distinct, and is due beyond doubt to the activi- 

 ties of the hyaline ectoplasm, which is accumulated espe- 

 cially at the angles of the cells. It there forms extremely 

 fine filamentous pseudopodia, through the activity of 

 which the cells may change their shape or move from place 

 to place. The exact character of the movement is not 

 the same in all kinds of cells and it varies greatly in inten- 

 sity. Axial mesoderm and medullary cord yield cells 

 that frequently wander for considerable distances by them- 

 selves; epidermis, when it does not roll up into bands or 

 spheres, may form a hyaline fringe, and spread out con- 

 siderably; pieces of the central nervous system and the 

 primordia of the cranial ganglia give rise to the fibre-like 

 structures described in the last section; the endoderm and 

 notochord remain almost inert. 



In passing, I should like to refer to two points which 

 baffle students of tissue-culture. I offer an interpretation 

 of them on the basis of my knowledge of ectoplasmic 

 behavior in general. 



The first concerns the observation so often noted that 

 living cells in tissue-culture tend to assume a spindle- 

 shape, especially when they migrate from the bit of tissue 

 implanted in the culture-medium. There is no correlation 

 between the original form of the cell and the spindle-form 

 subsequently attained as we can conclude from the studies 

 of many observers, who on various types of cells have con- 

 firmed Harrison's original observations. Two suggestions 

 have been offered : that the spindle-form is a reversion to a 

 less differentiated (i.e., embryonic) cellular condition and 

 that it is the effect of the cell's new, and abnormal, environ- 

 ment. My suggestion is that the spindle-shape expresses 

 gain in ectoplasm. I base this view on the fact that cells 

 when isolated usually show relatively more active ectoplasm 

 than when they are in contact and further on the observa- 

 tion made by Harrison that spindle-shaped cells become 



S5 



