DIPS INTO MY AQUARIUM. 27 



in the centre of the Desmid may be seen gradually enlarging, 

 without, however, the fracture of the membrane. In the course 

 of two or three hours the two halves are separated, each com- 

 mencing to grow, and continuing till the parent form is reached. 

 Another method of reproduction is that called conjugation. Two 

 individuals approach each other, and at length mingle their 

 contents together, after which a circular body makes its appear- 

 ance, called a sporangium — that is, a spore- vessel. At length 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 anyone, but complete success has never been 

 attained. He used a mixture of pure alcohol, distilled water, and 

 glycerine, which being nearly of the same specific gravity as 

 water, retards the contraction of the cell. I have had several 

 specimens in my cabinet for some years which have not appreci- 

 ably 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, for an indefinite 

 period, of evaporation. 



P"ig. 2. Volvox globator. 



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 rest- 

 less eagerness of nineteenth-century science has not solved. It is 



