ANIMALS FOR. 49 



Fig. 9. This species is very common, and forms 

 an interesting inhabitant in an Aqua vivarium. 



Care must be taken, 

 however, not to place 

 it in the same jar with 

 fishes, or other crea- 

 tures which might 

 make it their prey. 

 The membrane which 

 surrounds the body, 

 and contains the air, is 

 transparent, so that the 

 spider looks in the 

 water as though its 

 body was composed of 

 nothing but a bubble 

 of air. It is very active, and is a most amusing 

 creature. 



The Crustacea, the family to which CRABS, LOB- 

 STERS, and SHRIMPS belong, have not so many 

 representatives in fresh as in salt water ; at the 

 same time, a large number of species are common 

 enough in our fresh waters. The largest of our 

 fresh-water Crustaceans is the Common Biver Cray- 

 fish (Astacus fluviatilis). It is found in almost all 

 the rivers and larger streams of Great Britain, and 

 is brought to London in considerable quantities as 

 an article of food. I have often bought them at 

 the fishmonger's, but must confess to not having 

 succeeded in keeping them alive. My friend 

 Dr. Ball, of Dublin, however, succeeded in keeping 

 one for some time ; and Professor Bell, in his 

 classical work on the Stalk- eyed Crustacea of Great 

 Britain, has given the following account of his pet 

 from Dr. Ball. " I once had a domesticated cray- 

 fish, which I kept in a glass pan, in water not more 

 than an inch and a half deep ; previous experiments 



