NATURAL HISTORY OF BHOMPSTON POND. 227 



Another alga is Vaucheria (fig. 98), a branched filamentous 

 but non-cellular form. It contains very numerous chlorophyll 

 granules, and the nuclei increase by division as the filament 

 grows apically. It reproduces asexually by the formation of 

 a zoosporangium (a) at the end of the filament ; the contained 

 ciliated zoospore (a compound of a number of small bi-ciliated 

 zoospores) escapes, giving rise to a new filament with a colour- 

 less rhizoid. Sexual reproduction also occurs, spherical 

 oogonia and tubular antheridia sometimes being found. 



PART 2. 

 ZOOLOGY. 



The foregoing account deals only with those forms of life 

 found entirely submersed. But for many the damp and 

 muddy pond-side is the natural habitat ; for some, however, 

 the surface of the water provides a more suitable environment, 

 while others prefer to flit above the pond. The most typical 

 of these, together with some partly submerged plants, must 

 now be briefly mentioned, as their presence, or very existence, 

 more or less depends on the pond. 



The well-known Hydrometra stagnorum (Fig. 61) is found 

 actively running on the surface of the water by means of its 

 long and slender legs. The head and thorax are very elongated 

 the former bearing a pair of rather long antennae ; and a 

 pair of small but distinct eyes. 



Close at hand was found a group of whirligig beetles 

 (Gyrinidce) darting about very rapidly on the surface of the 

 water, their tiny glossy wing-cases shining in the sunlight. On 

 closer examination each eye was found to be divided into two 

 parts, so that the beetle appeared to have four eyes ; the 

 antennae had a fusiform clubbed extremity. A host of 

 other beetles occur around the pond, a characteristic species 

 being Elaphrus uliginosus (fig. 71), a little carnivorous ground 



