288 THE PHENOMENON OP 



of the inmost lamella of the cell-membrane in the forma- 

 tion of the reproductive cell. 



a. With ladder-like (scalariforni) yoke-conjugation. 



a. The spore in the connecting canal or middle piece 

 of the double cell. In Zygogonium* 



|3. The spore in one half of the double cell (in the 

 cavity of one of the two conjugating mother-cells). 

 Ordinarily the case in Spirogyra,\ and Zygnema.% 



y. A spore in each half. This case occurs only as 

 abnormal in Spirogyra, and appears to depend upon an 

 incomplete carrying through of the conjugation, the 

 union-processes coming into contact, but not anas- 

 tomosing. 



b. With fence-shaped (ffeniculate] yoke-conjugation. 



a. The spore in the uniting canal or middle piece. In 



|3. The ^pore (or the gonidium) in one of the halves of 

 the double-cell. Here belong Sirogonium*^ with a spore 

 formed exactly as in Spirogyra^& the genus Mougeotia** 

 still enigmatical in its mode of reproduction, probably 

 possessing an active gonidium, leaving the mother-cell 

 directly after its formation. 



c. Chainlike (catenate] union of the cells of the same 



The spore in the lateral connecting-canal of the 

 conjugated-cells. This case is not yet known, but it is 



* Vaucher, 'Histoire des Conferves,' t. vii, f. 34; Hassall, 1. c., 

 t. 39. 



f Vaucher, 1. c., t. iv and v ; Hassall, 1. c., t. 18, 25, and 2732. 



j Vaucher, 1. c., t. vi, f. 4; t. viii, f. 1, 2; Hassall, 1. c., t. 38. 



Vide Kiitzing, 'Phyc. General,' t. 15, f. 1, 3, 4, 6 (of Spirogyra 

 quinina. 



|| Hassall, 1. c., t. 4245. 



f Hassall, 1. c., t. 26. 



** Hassall, (1. c., p. 172,) indeed, asserts that Hougeotia is propagated by 

 zoospores, but gives no further information regarding their formation. 

 Vaucher (1. c., p. 79, t. viii) formed out otMougeotia the section " conjugees a 

 tubes interieurs," and describes the emergence of already elongated many- 

 celled young filaments from the old cells, a phenomenon which may be 

 explained as accidental development of gonidia remaining in the mother- 

 cell. 



