Desmidieoe.'] infusorial animalcules. 277 



same as in the Conjnriatce. Two fronds unite by means of pro- 

 jections arising at the junction of the two segments, and then the 

 newly fonned portion continues to enlarge until the original seg- 

 ments ai'e separated by a coll of an ii-rcgular four-sided figure. The 

 contents of the fronds, being collected in this cell, become a dense 

 seed-like mass, wliich is sometimes globular, resembling the Spo- 

 rangium of 3Iongcotla, and sometimes square, like that of Stauro- 

 S2)ennnm. The ne^ly-formed cell is thinner, and generally paler 

 than the segments of the frond ; in some species it looks like a pro- 

 longation of the segments, and in others these are so loosely attached, 

 that their coimection is scarcely perceptible. (P. 13. f. 5, 6.) 



The coupling of the fronds generally takes place from the convex 

 margin, but may occiu' on the concave, or even the convex margin of 

 one frond may couple with the concave of the other. 



The Rev. W. Smith has presented to naturalists an excellent ac- 

 count, with a series of illustrative engravings, of the phenomena of 

 conjugation in Closterium Ehrenhenjin, which he states differs from 

 those in other Closteria generally, and indeed from those of any 

 other of the Besmidiccs. (AnnalNat. Hist. vol. 5, 1850.) 



" The first phenomenon is an alteration in the granular condition of 

 the endochrome. This, from a light yellowish green, passes to a 

 much darker shade, and the larger granules, or " diaphanous vesicles" 

 of Ealfs, which were originally few in number, and arranged in a 

 somewhat irregular longitudinal series (P. 18, f. 10), become exceed- 

 ingly numerous and pervade the entire frond. While this change is 

 about taking place, the fronds approach in pairs, approximating by 

 their concave surfaces, and finally coming into such close neighbour- 

 hood that their inflated centres are in contact, and their extremities 

 slightly overlapped. (P. 18, f. 11.) In a short time, probably in 

 the course of twenty-four hours, a remarkable change takes place, 

 both in the appearance and condition of the fronds ; a mass of 

 delicate mucus is secreted around the approximated fronds ; these 

 remove to a little distance from each other, undergo ' self-division ' 

 and present altogether an irregular oval figure, the outline of which 

 is formed by the periphery of the mucus, the four divisions of the 

 fronds being placed in the middle in a somewhat quadrilateral 

 manner. (P. 18, f. 12.) During the progress of cell-division, the 



