38 



NATURAL HISTORY OF THE FARM 



limpct-shapcd. Two of these are sliown in 

 ^ Figure i<;. In all of them flaring margins 

 ^•S of the body fit down closely to the stone and 

 V^ deflect the water, so that it presses them 

 J^ against their sui)]X)rt. 



In still water the deep pools are the 



Pic. 19. Two 



in«H:t hirvae that spccial homc of thc larger fishes. We shall 



stick to stones m ^ ^ 



rapidwatrr: a. the rctum to thcm in thc next study. In the 



flat nmc- tuctle 



^ui'-^b^^'thJ^n^cV s^^^^r parts and in the midst of the aquatic 

 vdncfi midge (BU- vcgctation arc the lesser fishes and many other 

 familiar vertebrates, frogs and their tad])oles, 

 salamanders, turtles, etc., of uncertain occurrence. Much 

 more generally distributed and constantly present are a 

 few molluscs and crustaceans, such as are shown in Figure 

 20. There are a few adult insects (fig. 21) and many insects 

 in immature stages (figs. 22, 23) and 24. Some help toward 

 the recognition of these may be had from the table on pages 

 40 and 41, which contains brief hints, also, of the situation 

 they occu])y in the water and the role they play in the food 

 consumption. 



There are leeches, and fresh-water sponges and bryozoans, 

 and a host of lesser forms of many groups, mostly too small to 



r/fcsryir£'iyvs 



MOL L usc:> 



Fig. 20. Some common crustaceans and molluscs: crawfish, with the asellus at 

 thc I'^ft and the scud (Gammarus) at the ri^ht; — also, a mussel and two snails; 

 (LimiKta, on the left, and Planorbis on the right). 



