104 SUMMARY OF CURRENT RESEARCHES RELATING TO 



in which tliey swarm actively ; each vesicle is attached to the sub- 

 stratum by two very delicate threads. Each cell has two cilia, 

 abundant cellulose, a starch-grain, red eye-spot, and two alternately 

 pulsating vacuoles. After a time the vesicle bursts ; the cells swarm 

 free, then become immotile, and enter into a palmella-condition, a 

 number being inclosed in a common gelatinous envelope. They 

 divide, like Palmella, and each cell ultimately developes into a 

 microzoospore, closely resembling one of tho original cells. Several 

 alternate generations of zoospores and palmella-cells are produced in 

 the autumn and winter, and in the spring commences the sexual re- 

 production. Some of the palmella-cells are transformed into zoogo- 

 nangia ; out of the contents of each of these are formed from 4 to 16 

 zoogonidia, scarcely differing from the zoospores, but possessing 

 sexual properties, since some of them conjugate, the rest soon perish- 

 ing. The zygospores contain a red endochrome, and remain dormant 

 for a time. In the latter part of the summer they germinate, and 

 each produces one or less often two macrozoospores, which ultimately 

 attach themselves to another alga, become invested with an envelope 

 of mucilage, and develope, by the division of their contents, the 

 original colonies. The author considers the genus nearly allied to 

 the Volvocinese. 



Kentrosphcera. — Two species of this genus form green gelatinous 

 lumps in the midst of filaments of Oscillariese. These colonies are 

 composed of zoosporangia ; each sporangium is unicellular, about 

 200 iJL in diameter, with a very thick concentrically stratified wall of 

 cellulose, and often possessing on one side a protruding spur. The 

 cell contains bands of chlorophyll and a red pigment ; the bands dis- 

 appear, the cell becomes uniformly green, and the contents break up 

 into a great number (about 400) of zoospores ; they are minute and 

 biciliated, but possess no vacuole or eye-spot. After swarming they 

 become fixed, and develope into spherical cells, which divide inter- 

 nally into the protococcoid colony. Many of these colonies may 

 follow one another in succession. No sexual mode of propagation 

 is known. Kentrosphcera probably belongs to the Palmellacefe. 



Hormotila. — H. mucigena, the only species, covers with a thick 

 green incrustation the walls of water-basins and damp rocks round 

 Messina. Its vegetative form is scarcely distinguishable from a 

 Glceocystis ; the cells, very unequal in form and size, are imbedded 

 in mucilage. Eeproduction takes place only by means of zoospores, 

 and apparently at all times of the year. To form zoosporangia, 

 certain of the cells separate from the rest, and lose their mucilaginous 

 envelope. These divide repeatedly by bipartition, and thus form 

 small branched tufts bearing an external resemblance to Gladophora. 

 In each of these cells are formed from 8 to 64 minute biciliated 

 zoospores, which escape through the lateral protuberance in the wall 

 of the mother-cell. After swarming they either develope directly 

 similar tufts of sporangia, or, more often, pass through the gloeocystis- 

 condition first. The genus must be regarded as belonging to the 

 Palmellacese. 



