AMCEBOID MOVEMENT OF SPONGE CELLS. 159 



many fluctuations. Even a fast moving cell sometimes stops 

 and after a short period of rest resumes its movement. The 

 retardation as a rule takes place when the cell changes its direc- 

 tion. The average velocity of an archaeocyte measured in ten 

 different experiments varied from .6 to 3.5 microns per one 

 minute; the maximum velocity was as great as 20.0 microns per 

 one minute. This maximum velocity was observed only twice. 

 The distance travelled varied from 64 to 185 micrones and active 

 movement lasted from 40 to 168 minutes. 



THE BEHAVIOR OF THE DISSOCIATED CELLS IN A 

 COMPOUND SUSPENSION. 



The cells of two different species of sponges mixed together 

 coalesce only with cells of their own species. This ability of 

 cells to discern the more foreign elements can be easily observed 

 when two sponges of different colors are used. Wilson (1910) 

 pointed out that the cells of Microciona mixed with those of 

 Lyssodendrix and Stylotella form different clumps each apparently 

 composed of the cells of same species; the clumps could be 

 recognized by their natural colors. The same was found by the 

 writer when a mixed suspension of Reniera informis, violet, 

 Reniera densa, gray, and of Microciona, red, and Cliona, yellow, 

 were tested. The aggregates formed in such emulsions were a 

 violet, gray, red and yellow. 



It is quite easy to distinguish the colors of the aggregates but 

 as the color of a single cell is very slight it is impossible to dis- 

 tinguish the species while the cells are in suspension. In order 

 to find how complete is the separation of the cells in a mixed 

 suspension, one of the sponges before the experiment was fed 

 with carmine, the other, with Chinese ink. The red and black 

 granules ingested by the cells serve as definite marks indicating 

 the species. 



The suspension contained the cells of Reniera informis fed with 

 carmine and that of Reniera densa .fed with Chinese ink. The 

 resulting aggregates lying close together consist exclusively 

 either of carmine or of ink laden cells. The same occurs in a 

 mixture of Microciona prolifera and Cliona celata. 



Coalescence with the cells of another species never occurs even 

 when the cells are artificially pressed together by centrifuging a 



