ARTHROPODA 83 



In addition to the above the Malacostraca in- 

 clude the Arthrostraca, or crustaceans which have 

 the front of the body jointed as well as the tail, 

 so that there is no large shield formed by the 

 fused armour of several segments (cephalo-tho- 

 racic shield, cf. Figs. 16 and 17), as in crabs and 

 lobsters. The Amphipoda, or Sand - hoppers, 

 sometimes called Sand-fleas, are familiar examples 

 of these. There are several common kinds found 

 on our English shores, and sometimes they ap- 

 pear in such numbers, hopping above sand or sea- 

 weed left by the tide, that they seem to form a 

 sort of cloud, every unit of which, however, is 

 but in the air an instant, falling and giving place 

 to some other, while 

 it prepares for a 

 fresh hop. The so- 

 called Freshwater 

 Shrimp, Gammarus, 

 is another common 

 m*>mHAr nf the* Am FlG - l8 - A Sand-hopper, Pallasea 

 u ^ S o CanceUus, from Siberia, natural 



phipoda. Fig. 1 8 size, 

 shows the general 



form of a Sand-hopper. Nearly allied are the 

 Isopoda or Wood-lice, interesting because they 

 are among the few terrestrial forms of the crus- 

 tacea ; they live, however, in damp places, and 

 are but too well-known in gardens, where the 

 gardener often mis-names them " insects." 



The mention of terrestrial forms would natu- 

 rally bring us to the discussion of the true In- 

 sects. In the Arthropoda we for the first time 

 meet with terrestrial animals except in scattered 

 instances, and the true Insects are the largest 

 and most important group of these. There are, 

 however, various creatures belonging to the 



