BRANCHIOPODS. 167 



more than two lines in length, it is, from its habits and its rapid multiplication, very 

 destructive. It pierces the planks of ships in every direction with alarming rapidity, 

 and in sea-ports and dockyards its ravages are very serious. "When seized, it rolls itself 

 up into, a ball. 



The Cliehtra tcrcbrans is another timber-destroyer, 

 equally formidable. It excavates the wood, not merely 

 for the purpose of concealment, but with the object of 

 employing it as food. It will freely attach itself to a piece 

 cf wood placed with it in a glass of water, so that its habits 

 may be studied in confinement. Timber which has been 

 subjected to the ravages of Chdnra presents a somewhat 

 different appearance from that which has been attacked by FlG - 16 9 -LirtuoMA 

 Limnoria terebrans. In the latter we find deep cylindrical 

 grooves running deep into the interior, while the excava- 

 tions of Chelnra are consideral 1; larger and more oblique in their direction, so that the 

 >urface of the timber thus undermined by those animals is rapidly washed away by the 

 action of the sea, and the excavations are exposed in the greater part of their extent, 

 the wood appearing ploughed up, so to speak, rather than burrowed into. Upon the 

 \.hole, C/it'/iua would seem to be a more destructive creature than even Limnoria. 



The Fresh-water Shrimps (Aselhis] are met with abundantly in our 

 ponds and streams. They walk with difficulty, but swim rapidly, lying on the 

 side. The eggs of the female are carried in a bag attached beneath the body. 

 They are very voracious, and as they eagerly devour all dead animal sub 

 stances, are beneficial agents in purifying the water. 



The "Wood- Lice (Oniscus) are terrestrial in their habits. They are to be 

 met with everywhere in dark and damp situations, such as caverns, cellars, in 

 holes in old walls, under stones or beams of wood, window-sashes, and similar 

 localities. They feed entirely upon decayed animal and vegetable substances, 

 and never leave their retreat except in rainy or damp weather. 



GILL-FOOTED CRUSTACEANS. ORDER BRAXCHIOPODA.* 



Any one who has ever examined a phial of water taken from 

 any ditch must have observed in- it a variety of tiny but most 

 indefatigable little creatures, that move actively by short jerks, 

 or dart to and fro with a rapidity that the eye can scarcely follow. 

 The jerking ones (Fig. i/o, 3) are species of Daphnia ; the more 

 fleet, darting forms are of the genus Cyclops (Fig. 170,1); and 

 another tribe, still more varied' in shape, that keep chiefly near 

 the bottom, and creep nimbly more than they swim, are the Cy- 

 prides (Fig. 170, 2): all these, under a microscope, are exceedingly 

 beautiful Some have their bodies enclosed between two delicate 

 plates, united above the back, and resembling a bivalve shell; 

 this shell is usually more or less transparent, and delicately tesse- 

 lated, or marked with an intricate network of raised lines. The 



* Ppdvx ia > branchia, gills ; TTOVS, 7ro56s, pous, podos, a foot: so called because their feet 

 perform the iunctions of gills. 



