1886.] 



MICROSCOPICAL JOURNAL. 



Ill 



the process of forming new families 

 within the mother-cells.] 



40. Genus Sorastrum Kutzing. 

 CaMiohiimi globose, solid within, 



formed of 4-8-16 or more radially 

 arranged, wedge-shaped, or com- 

 pressed-cuneate cells, with sinuate or 

 concave margins and bifid at the cor- 

 ners. Propagation unknown. 



[This genus resembles Stauroge- 

 nia^ and is usually placed near to it 

 in systematic works. Kirchner, how- 

 ever, places this genus here, probably 

 because of the definite character of 

 the coLMiobium.] 



41. Genus Selenastrum Reinsch. 

 Cells semilunate or almost sickel- 



shaped, joined together at the middle 

 of the convex surfaces, in spherical 

 families of 4-8 cells. Propagation 

 •unknown. 



[It is by no means certain that this 

 genus is not more closely associated 

 with Raphidbim^ (5,) but the ar- 

 rangement of the cells in families, 

 although somewhat variable in dif- 

 ferent species, is rather more definite 

 than in Raphidium.^ 



42. Genus Coelastrum Nageli. 

 Cnenobium spherical, hollow, 



formed of a single layer of cells, with 

 clear spaces interspersed between 

 them. Cells angular by mutual pres- 

 sure or spherical. 



Macrozoospores form a new coeno- 

 bium within the mother-cell, which 

 is set free by ruptmx' of the latter. 



43. Genus Pedlastrtini Meyen. 

 Coinobium flat, disk-like, formed 



of 8-16-32 cells. Cells angular, 

 those in the periphery truncate at 

 the base and dilated outwards, notched 

 in the middle of outer margin. 



Propagation by micro- and macro- 

 zoospores. Macrozoospores formed 

 by repeated division of one cell of the 

 family. They come out from the 

 mother-cell enclosed in an envelope, 

 within which they arrange them- 

 selves, after they have come to rest, 

 into a new coenobium. The micro- 

 zoospores form in the same wav, but 

 in greater number, escape from the 

 mother-cell, and swarm about in the 



water ; nothing further is known of 

 them, but they probably conduct 

 themselves like those of Hydrodic- 

 tyon. 



\_Pediastrum resembles a round or 

 oval desmid, but it differs in being 

 made up of several distinct cells form- 

 ing a coenobium.] 



44^. Genus Hydrodictyon Roth. 



Coenobium consisting of many 

 large, cylindrical cells, so united by 

 their ends as to form a closed net of 

 numerous polygonal, usually pento- 

 ganal meshes. 



Propagation by macro- and micro- 

 zoospores. Macrozoospores pear- 

 shaped, with two cilia in great num- 

 ber within the mother-cell, where 

 they remain for some time in active 

 motion, then join together and form 

 a net like the parent, which escapes 

 by the solution of the cell-walls, and 

 grows to a large size. 



Microzoospores form in like man- 

 ner in great numbers within a mother- 

 cell (as many as 30,000), each with 

 4 cilia. They escape through a late- 

 ral opening, swarm about, and may 

 copulate. After copulation they come 

 to rest, and form spherical cells, re- 

 sembling ProtococcKs. After a long 

 time, and dessication, their contents 

 produce 2-5 large swarm-cells with 2 

 cilia, which escape, and after swim- 

 ming about come to rest. They then 

 grow to large, angular, irregular cells, 

 with points or horns at the angles 

 {polyedern Pringsheim) , which pro- 

 duce new nets by division of their con- 

 tents, in the same manner as in the 

 propagation by microzoospores. 



[The nets of Hydrodictyon may 

 grow to a length of 12 inches or more. 

 They are common in ponds almost 

 everywhere, most abundant in June 

 and July.] 



Family III. Volvocace^ Kirchner. 



Vegetative cells during their entire 

 life in motion, by means of cilia. 

 Propagation sexual, or by copulation 

 of swarm-cells, or asexual. 



In accordance with present knowl- 

 edge the family is divided into — 



