100 ZYGOPHYCEJE. 



spore ; nevertheless we have not followed Wittrock in uniting Mou- 

 geotia, Mesocarpus, Pleurospermum, Craterospermum, and Stauros- 

 permwn under the one genus, HfoiM/eotia,, because we think that there 

 are sufficient characters to warrant the retention of Staurospermum 

 apart from Mesocarpus. If the mode of development in the following 

 two species is accurately appreciated, this genus is more allied to Zygo- 

 ffonium than Mesocarpus. See Archer in Quart. Micro. Journ., 1866, 

 p. 271. 



XVXougeotia glyptosperma. DeSary Conj. p. 78, t. 8,f. 20-25. 



Sterile cells 7 to 12 times as long as broad. 



Zygospores large, oval, with a thick, firm, yellow-brown 

 epispore. 



Sporiferous cells elongated. 



SIZE. Cells 'Ol-'Olo mm. 6 to 10 times as long. Zygo- 

 spore -016X-035 mm. 



Rabh. Alg. Enr. iii. 255. Archer in Quart. Journ. Micr. 

 Sci. 1866, p. 65. 



As pointed out by Mr. Archer (loo. cit.) " this plant is not truly a 

 Mesocarpus, but in its mode of conjugation more nearly approaches 

 certain Zygnemata. It is no doubt related, on the one hand to Meso- 

 carpus (Hass.) ; like it the endochrome forms a compressed longitudinal 

 band, and like it too, the zygospore is formed half-way between the two 

 conjugating joints. But, it is distinguished strongly by the fact that 

 here the whole cell contents 'primordial utricles' and all, of the two 

 conjugating joints completely coalesce, leaving the old cell-walls empty, 

 in order to form the zygospore ; whilst in Mesocarpus the contact of the 

 primordial utricles of the two conjugating cells is not followed by a 

 complete coalescence of the two into the zygospore ; but by a concen- 

 tration of the principal part of the green and solid contents in the con- 

 necting canal half-way between the two joints, and the shutting off 

 thereupon of the residue of the pale granular contents remaining in each 

 parent joint, the denser central portion becoming the spore, and that 

 cut off on each side eventually becoming effete and lost. Hence in 

 Mougeotia glyptosperma the spore is the actual result of the complete 

 fusion of the entire cell contents of the two conjugating joints it is 

 the true zygospore ; whilst in Mesocarpus the ultimate spore is a 

 daughter. cell, as it were, of the zygospore. Therefore, on the other 

 hand, the present plant shows an affinity to Zygnema ; but it is, of 

 course, completely distinct in the flattened band of endochrome, not 

 doubly stellate, as in that genus, not to speak of the extremely different 

 comparative length of the cells, which, within the limits of each, is 

 constant." 



Plate XLI. fig. 1. a, sterile cells X 400 ; b, c, conjugatiag cells with 

 zygospores, after De Bary, X 200 ; d, zygospore, after DeBary, X 400. 



Mougeotia lesvis. Archer Micr. Journ. 1867 t. 8, f. 1-3. 

 Sterile cells twice as long as broad. 



Zygospores broadly elliptic or oval. Epispore thick, brown. 

 Sporiferous cells sometimes elongated. 



SIZE. Cells -02--25 mm. Zygospore about -045 x -036 mm. 

 Rabh. Alg. Eur. iii. 255. Archer Micr. Journ. 1866, p. 270. 

 Zygogonium Iceve, Kutz. Tab. v. t. 13. 



In ditches and pools. 



