36 THE MICROSCOPE 



which become detached from the plant. But in other cases 

 special supports or receptacles are formed in the Thallus, the sole 

 function of which is to produce Gonidia, either by the abstriction 

 of the ends of special branches (Stylogonidia), or by free cell for- 

 mation in the interior of large cells (Endogonidia). The Gonidia, 

 when they escape from the mother cell, possess no cell-wall, and 

 are motile ; hence, they are now called Zoogonidia. The anterior 

 end is hyaline, and in some cases a minute red dot lies at one 

 side ; two cilia are attached to the anterior end, or to the side, or 

 to both. Sometimes the anterior end is encircled with cilia, or 

 even the entire surface of the Zoogonidium. 



During swarming a cell-wall is secreted, the Zoogonidium 

 comes to rest, attaches itself to some body by its anterior end, 

 the cilia disappear, and germination commences, the end which 

 was posterior during swarming now becoming the growing point, 

 and hence the anterior end of the young plant. 



It is well to mention here that in some cases swarming cells 

 are seen to conjugate ; in this case they cannot be regarded as 

 Zoogonidia, but as motile sexual organs which should be placed 

 in the class Zygosporese. 



It must not be supposed that all the Fresh-Water Algae are 

 reproduced exactly according to one or other of the methods now 

 described ; on the contrary, although allowing of a general classi- 

 fication under one or other of these heads, there is very great 

 diversity amongst them, the details of which it would be impos- 

 sible to give within a reasonable length. Taking, however, this 

 classification as a basis, in our next paper, we will glance at 

 some of the principal genera. 



^be fIDicroecope an& bow to use it 



By V. A. Latham, Late Hon. Sec. U.J.F.C., Norwich. 



D 



Part V. — Double-Staining, etc. 



OUBLE-STAINING is a subject which requires to be very 

 much more worked out than it has been hitherto. There 

 is no pursuit in which patience and time for experimenting 



