26 • DIPS INTO MY AQUARIUM. 



slip of glass for inspection. Most Desmids are free cells, but in 

 some cases several individuals are grouped together in the form of 

 a star or disc. Others, again, take the form of long threads or 

 ribbons, and are consequently called filamentous Desmids (e.g., 

 Hyalothecd). 



Desmids possess a transparent, membranous envelope or case, 

 entirely destitute of silica, the flinty material which accompanies 

 diatoms. This case contains the chlorophyll, or green colouring 

 matter, which renders these tiny plants so conspicuous. They no 

 doubt constitute the chief food of fresh-water animalcules, and 

 almost every observer of them has seen the rotifer greedily suck 

 out the contents of the envelope and cast away the empty, but 

 still beautiful case. While living they have the power of gliding 

 through the water with an even, graceful motion, while their 

 hyaline covering, sparkling with emerald points and filled with 

 diamond-like granules, make up a vision of beauty surpassing 

 that which Aladdin's lamp revealed. 



What gives to the plant this power of independent movement ? 

 Does it possess tiny hairs, or cilia, with which it lashes the water, 

 or rows itself along, or is the cause to be found in the generation 

 and exhalation of oxygen ? Here is a question which I have to 

 confess I am unable to answer, although I have peered at these 

 fairy-like organisms with prolonged and tireless curiosity through 

 almost the best optical apparatus that science can supply, and I 

 could wish my readers no better fortune than that they might hit 

 upon this well-guarded secret of Nature. For those who possess 

 good appliances, I would suggest this problem for their study. 

 The Desmid should be carefully observed on a dark back-ground, 

 with and without a condenser, in a natural condition, and also 

 stained with aniline dyes. But these are details into which I 

 have promised not to enter now. 



It is not difficult to cultivate Desmids. They should be kept 

 in a watch-glass, filled with their own native water, and covered 

 with a plate of glass to keep out dust and prevent too rapid 

 evaporation. If absolutely necessary to renew the water, a little 

 rain-water should be added. 



There are two methods by which Desmids reproduce them- 

 selves. The first is by cell-division, or fission. The clear space 



