Pond Animals 



337 



(3). The lumps of brownish gelatin inclosing com- 

 pound colonies (Rivularia, see fig. 52 on p. 134, etc.), 

 that are likely to cover the same stems later in the 

 season, and that sometimes seem to smother the green 

 vegetation. 



(4). The spherical lumps of greenish gelatin that lie 

 sprinkled about over the bottom rather hard lumps 

 inclosing compact masses of fila- 

 ments of Nostoc, etc. 



(5). The accumulated free- 

 swimming forms that are not 

 seen as discrete masses, but that 

 tint the water. Volvox tints it 

 a bright green; Dinobryon, yel- 

 lowish; Trachelomonas, brown- 

 ish; Ceratium, grayish, etc. 



Such differences as these in 

 superficial aspect, coming, as 

 many of them do, with the regu- 

 larity of the seasons, suggest to 

 one who has studied them the 

 principal component of the 

 masses ; but one must see them 

 with the microscope for certain 

 determination . 



The animals of the pond that breathe free air are a few 

 amphibians (frogs and salamanders), a few snails 

 (pulmonates) and many insects. The insects fall into 

 four categories according to their more habitual posi- 

 tions while taking air: 



(i). Those that run or jump upon the surface. 

 Here belong the water-striders and their allies long 

 legged insects equipped with fringed and water-repel- 

 lent feet that take hold on the surface film, but do not 

 break through it. Here belong many little Diptera that 

 rest down upon the surface between periods of flying. 



FIG. 197. Diagram of a lily- 

 pad, inverted, showing 

 characteristic location and 

 arrangement of some 

 attached egg clusters. 



a, Physa; 6, Planorbis; c, Trias- 

 nodes; d, Donacia; e, Hydro- 

 campa; /, Enallagma (inserted 

 into punctures) ; g, Notonecta 

 (laid singly) ; /;, Gyrinus. 



