1886.] 



MICKOSCOPICAL JOURNAL. 



51 



sides of aquaria, where they appear 

 as small, ciixular specks.] 



IV. ORDER ZYGOSPORES. 



Cells free or in filaments, green or 

 brown; reproduction by a special 

 act of copulation or conjugation, in 

 which the contents of two cells of 

 similar form unite to form a single 

 primordial cell, which becomes 

 clothed -with several envelopes and 

 forms a zygospore. 



Without copulation an azygospore 

 mav be produced. Asexual propa- 

 gation by repeated division in the 

 same direction. No s'warm-cells. 



FAMILIES. 



Single cells or filaments un- 

 branched. Conjugate X. 



Unicellular, silicious. 



Bacillariace^ XI. 



The family Bacillariacefe will be 



omitted from this classification, as 



will be also the desmids which have 



. already been so well treated by Mr. 



Wolle in his excellent book. 



JPajtiily X. CoNjUGAT.-E. 



Cells single, free, or united in fila- 

 ments, w^ith green contents ; chloro- 

 phyll in bands on the cell-walls, in 

 axillary plates, or in pairs of radiate 

 masses. Walls not silicious. 



A. Zygneme^. Group i. 



Cells cylindric, confervoid, light- 

 green, in somewhat gelatinous fila- 

 ments. The zygospore forms three 

 successive coats on its surface ; the 

 outer being thin soon disappears, 

 leaving the middle thick coat as the 

 outside covering. A single plant 

 germinates from the zygospore, after 

 a period of rest. 



a. Zygnemin^. Sub-group i. 

 Chlorophyll in parietal bands, two 

 stellate masses or a single axial 

 plate. Copulation of two cells in 

 three ways : — 



1. Ladder-like or scalariform, in 

 which lateral projections from two 

 parallel filaments grow together, 

 their ends meeting, forming a ladder. 



2. Geniculate, in which two 



neighboring cells bend until the con- 

 vex sides come in contact. 



3. Lateral, in which two adjacent 

 cells of the same filament are united 

 by lateral outgrowths from each. 



In either case the t^vo cells become 

 united by the dissolution of the cell- 

 walls at the point of junction, so 

 that their contents commingle and a 

 zygospore is formed, either in one of 

 the cells, or between them in the con- 

 necting tubes. 



b. Mesocarpin^. Sub-group 3. 



Cells cylindric, with axial chloro- 

 phyll plates. Copulation, scalari- 

 form, geniculate or lateral, the zyg- 

 ospore never formed of the entire 

 contents of the copulating cells, but 

 is separated in the middle of the 

 double cell as a thick spore, colored 

 green by the entire chlorophyll of the 

 cells, enclosed by two or four mem- 

 branes. 



[In the Zygneminae the zygospore 

 is formed directly by the conjugation 

 of two cells, and the commingling of 

 their entire contents, which, gather- 

 ing into a spherical mass, becomes 

 covered by membranes, and passes 

 into a resting condition. This is the 

 typical zygospore, the same as is 

 produced by desmids and diatoms. 

 In the case of ladder conjugation, 

 for example, in this group, the two 

 cells unite to an H-shape, and the 

 contracted zygospore forms free with- 

 in one of the cells, or in the connect- 

 ing tube. 



In the Mesocai'pinae the process is 

 quite dift'erent. The conjugation of 

 the two cells forms the zygospore 

 without any contraction of the con- 

 tents, the two conjugating-cells to- 

 gether being regarded as the zyg- 

 ospore, which is the shape of the 

 united cells ; then in the case of lad- 

 der-like conjugation the zygospore is 

 H-shape and not contracted. But the 

 zygospore remains only a short time 

 in this condition. The colored por- 

 tion of the protoplasm passes into 

 the connecting-tube and becomes sur- 

 rounded by a membrane which 

 also effects a division of the cruciate 



