POND LIFE. Ill 



plain, round, green globules, and after a time the yellov/ 

 bodies have become scattered, and the little things inside it go 

 swimming about by the aid of their long tails, like tadpoles. 

 They collect round the green globules, into which some of 

 them penetrate ; then a kind of husk grows round the globule, 

 which rests for a time and afterwards divides into a number of 

 smaller spores, each of which is competent to reproduce a 

 colony just like the original one. So that here again we have 

 small plants budding off from each other, and also the union 

 of two parts to produce a spore which gives rise to a new plant 

 exactly like the parent. 



But these are not the only plants in our ponds. There are a 

 number called Diatoms (Fig. i — lo), because they consist of 

 two equal parts ; in fact, they are constructed very like a pill-box, 

 one of these parts being a little larger than the other. In 

 many cases the walls are very beautifully sculptured, the pattern 

 varying so much that several thousand species have been 

 described, which can be distinguished by their different markings. 

 Now, these creatures have a habit of expanding, very much as a 

 pill-box would do if you lifted the lid partly off it, and when the 

 depth of the box had been about doubled, a division takes place, 

 and the two halves separate and form two Diatoms, where there 

 was only one before (Figs. 9, 10). Of course, the one just formed is 

 not quite so large as the original. But this process goes on again 

 and again, until a very small one indeed is formed ; two of these 

 meet together and split into halves, their contained protoplasm 

 escaping and fusing into a single mass (Figs. 2 — 6) with a husk 

 about it, and remains still for a time, and then grows to the same 

 size as the original Diatom, thus constituting what is called an 

 " increasing spore " {auxospore) (Fig. 6), and furnishing a means 

 for restoring the plant to the same size as the parent of the 

 family (Figs. 7 — 10), 



There is one other family of these low plants, which we call 

 Desmidiacece (Figs. 13 — 15), and which are found in enormous num- 

 bers in our ponds. The Desmid, like the Diatom, is divided into 

 similar halves. When reproduction is to take place, the two halves 

 separate a little from each other, and each one bulges out in the 

 centre (Fig. 13). Then a partition divides the bulged part into 



