3808 QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE, 
B. Conjugating-cells non-motile. 
DeEsmip1E#.—In 1836 Morren! published his account of 
the conjugation of Closterium (fig. 5), and was therefore the 
first discoverer of this process amongst the Desmidiee as now 
constituted. This important observation had as Morren him- 
self remarks for its not least important result the final sepa- 
ration of the species of Closterium from the animal kingdom 
to which they had been supposed to belong. ‘They were 
seen to agree in essential points notwithstanding their 
curious motility with the filamentous Conjugate, which no 
one ever doubted to be true plants. 
Diatomace#.—It was not till 1847 that Thwaites dis- 
covered conjugation (fig. 6) in this group which in many 
respects runs parallel with Desmidiee. 
Fie. 6.—Conjugation of Hunotia turgida with formation of two zygospores. 
A, front view of frustule; B, side view; C, side view of frustules, con- 
jugation commencing ; D, front view; E and F, side and front views 
after formation of zygospores (after Thwaites). 
ZYGNEMACEX.—Conjugation was discovered much earlier 
in the filamentous forms. It was first observed by O. F. 
Muller in 1782, and he figured in the Flora Danica (tab. 
883), under the name of Conferva jugalis, examples of a 
Spirogyra in a state of conjugation. ‘I'wenty years later the 
whole process was studied by a Swiss botanist, Vaucher, and 
described in his Histoire des Conferves d’eaux douces (1803), 
1 «Ann. des Se. Nat.,’ 2me sér., tom. v. 
