288 THE MICROSCOPE. 



an elongation of the membranous sac appear, giving a 

 semi-lunar sort of chamber ; this, as the eudochrome 

 elongates, becomes more denned, until it has the form and 

 outline of the chamber at the perfect extremity. The 

 obtuse end 6 of the frond is at the same time elongat- 

 ing and contracting; these processes go on ; in about five 

 hours from the division of the one segment from the other, 

 the appearance of each half is that of a nearly perfect 

 specimen, the chamber at the new end is complete, the 

 globular circulation exterior to it becomes affected by the cir- 

 culation from within the said chamber; and, in a few hours 

 more, some of the free bodies descend, become exposed to, 

 and tossed about in the eddies of the chamber, and the 

 frond, under a l-6th power, shows itself in all its beau- 

 tiful construction. E is a diagram of one end of a C. didij- 

 motocum, in which the same process was noticed. 



The Euasti"um Didelta is well worthy 



of attention, as well as many other species, 



the Xanthidium Penium, Docidium, <kc. 

 The Arthrodesmus Incus has a very 



beautiful hyaline membrane stretching 

 ^ from point to point, cut at the edges, 



something like the Micrasterias. This is 

 represented at fig. 157. 



The Mode of Finding and Taking Desmidiacece. As 

 the difficulty of obtaining specimens is very great, it will 

 materially assist the efforts of the microscopist to know 

 the method adopted by Mr. Ralfs, Mr. Jenner, and Mr. 

 Thwaites. " In the water the filamentous species resemble 

 the Zygnemata ; but their green colour is generally paler 

 and more opaque. When they are much diffused in the 

 water, take a piece of linen, about the size of a pocket 

 handkerchief, lay it on the ground in the form of a bag, 

 and then, by the aid of a tin box, scoop up the water 

 and strain it through the bag, repeating the process as 

 often as may be required. The larger species, Euastrum, 

 Micrqsterias, Closterium, &c., are generally situated at the 

 bottom of the pool, either spread out as a thin gelatinous 

 stratum, or collected into finger-like tufts. If the finger 

 be gently passed beneath them, they will rise to the sur- 

 face in little masses, and with care may be removed and 



