Tilden: pilinia and stigeoclonium. 617 



The cell under observation was 20 mic. long. After an hour 

 of active motion of the spores, its width was 18 mic. At this 

 point the wall at one side gave way. A spore passed out, 

 paused for a second, and darted away. The other seven then 

 followed in quick succession. 



A filament was observed while the spores were passing out 

 (PI. XXXIII. fig 9). From one cell four spores passed out, one 

 after another, through a break in the wall at the upper end of 

 the cell. Then almost immediately eight spores burst through 

 the end of the adjoining cell into the first cell and escaped 

 by the opening made by the former occupants. This indicates 

 that no particular area in the cell wall is thinner or in any way 

 specialised as the spot at which the spores shall break through. 

 Any portion of the end or side wall may serve this purpose. 

 The walls of the second cell were clearly outlined as shown in 

 the drawing. After the spores passed out there seemed to be 

 remaining very delicate membranes which had separated the 

 spores from each other. While the same thing was observed 

 several times, both here and in the Pilinia material, in many 

 instances there was not the least indication of it. All the spores 

 measured 5.5 mic. in diameter and 12 mic. in length. After 

 escaping from the cell and moving about for some time in the 

 water, they sometimes seem to gain in width and lose in length 

 — becoming broadly egg-shaped. 



A cell measuring 5 mic. at the end, 15 mic. in the swollen 

 portion, and 22.5 mic. in length contained seven or eight zoo- 

 spores (PL XXXIII, fig. 10). The cell wall seemed to be very 

 elastic, bulging out in different places as the spores changed 

 their position. They were more crowded, and for that reason, 

 probably, did not move so energetically as their neighbors. 

 They did not have the regular and mature form of those in the 

 adjoining cell. In their efforts to escape, the spores used their 

 ciliated end, which seemed to be slightly protruded like a pro- 

 boscis. 



Very often the last one or two spores in a cell do not escape 

 with the rest. This fact does not seem to be due to their cilia 

 being caught, since they move freely about in all parts of the 

 now roomy cell; but it appears that the walls after being burst 

 apart are again crowded together by some movement or con- 

 traction of the filament, before all the spores have a chance to 

 escape. 



After twelve days' culture indoors, the tanks were placed in 

 the open air, the water being changed morning and evening. 



