ISOPODA. 221 



FIFTH ORDER OF CRUSTACEA. 

 ISOPODA* (Similar-legged Crustaceans) 



Differ from the preceding in many important par- 

 ticulars. The two anterior feet are never annexed to 

 the head, but are appended to a distinct segment, 

 and furnished with simple pointed claws. In some 

 species which are terrestrial in their habits, two of 

 the antennae (the middle pair) are almost obliterated. 

 The females* carry their eggs attached to the under 

 part of their body, either enclosed by scaly plates, 

 or lodged in a membranous pouch. The young are 

 born in every respect resembling their parents, and 

 only change their skin as they increase their size. 

 The greater number live in the water, and those 

 Avhich reside on the land, require a certain degree 

 of dampness to enable them to respire. 



We select as examples of this order the redoubt- 

 able 



Boring Shrimps (Limnoria terebrans), so called from its habit of 

 boring into wood submerged beneath the surface 

 of the sea. Although this little creature is not 

 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 seaports and dockyards 

 its ravages are very serious. When seized, it rolls 

 itself up into a ball. 



The Chelura terebrans is another timber-destroyer, 

 equally redoubtable. It excavates the wood, not 

 merely for the purpose of concealment, but wit lithe 

 object of employing it as food. It will freely attach 

 itself to a piece of wood placed with it in a glass 

 of water, so that its habits may be studied in con- rsBEEBAKs 



finement. Timber which has been subjected to the 

 ravages of Chelura presents a somewhat different appearance from 

 that which has been attacked by Limnoria terebrans. In the latter 

 we find deep, cylindrical grooves, running deep into the interior, 

 while the excavations of Chelura are considerably larger and more 

 oblique in their direction, SD that the surface of the timber thus un- 

 dermined by these animals is rapidly washed away by the action of 

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



ftros, isos, equal ; ir6vs, pans, a foot. 



