184 RAMBLES AND REVERIES. 



jugation. Two individuals approach each other, 

 and at length mingle their contents together, after 

 which a circular body makes its appearance, 

 called a Sporangium, that is, a spore-vessel. 

 Ultimately a cloud of spores is poured out, and 

 from them a multitude of desmids ultimately 

 develop. 



Unfortunately, no medium has yet been discovered 

 in which these lovely objects can be preserved as 

 mounts, so as to retain their colour. Hantzsch, 

 of Dresden, has got as near to this desirable end 

 as any one, but complete success has never been 

 attained. He used a mixture of pure alcohol, dis- 

 tilled water, and glycerine, which, being nearly of 

 the same specific gravity as water, retards the con- 

 traction of the cell. I have had several specimens 

 in my cabinet for some years which have not 

 appreciably altered. But even this method of 

 mounting does not meet the difficulty of providing a 

 perfectly air-tight cell, which is, of course, absolutely 

 indispensable to the prevention of evaporation for 

 an indefinite period. 



Another object now claims our attention, and is 

 one that will richly repay careful inspection. This 

 is the ever-beautiful Volvox, familiar enough, but 

 enshrining deep mysteries that even the restless 

 eagerness of nineteenth-century science has not 

 solved. This is an object well worthy of being 

 sought after, and fortunately it can be obtained 

 at almost any time in the year. It is, however, 

 somewhat fickle in its attachments, for in localities 

 where it has been found repeatedly, it will at 



