334 



GENERAL BIOLOGY 



The alga Draparnaldia, 



shown in figure 187, which 

 grows attached to stones in 

 the riffles of small clear-flow- 

 ing permanent streams, and is 

 easily seen trailing its long 

 beautifully branching fila- 

 ments in the current, is a 

 favorable one in which to 

 - observe zoospore formation; 

 for it will usually develop 

 zoospores a day or two 

 after being brought out of its 

 native environment into the 

 laboratory. The spores, escap- 

 ing from the cells singly, will 

 swim to the lighted side of the 

 containing vessel, from the 

 surface of which they may 

 often be obtained in great 

 numbers. 



It will be noticed that the figure of the zoospore of Drapar- 

 naldia does not differ materially from that of certain of the 

 gametes we had before us in Chapter II. It is highly 

 probable that sex cells were developed out of zoospores. 

 Both are present in certain algae, and are hardly to be dis- 

 tinguished in form; and the differences between them almost 

 vanish, when, as sometimes happens, the gametes develop 

 without preliminary fusion in pairs. 



Multicell^ar reproductive bodies. In certain of the 

 lower fresh water animals, notably in sponges and bryo- 

 zoans, there are special multicellular reproductive bodies 

 called statoblasts (also known as winter buds, and gem- 

 mules). These are like spores only in function, and in hav- 

 ing resistant walls which tide them over the dry, hot 



FIG. 187. Draparnaldia, a, a bit of 

 the stem, with three branches; b, 

 a bit of a branch that is yielding 

 zoospores. 



