CRUSTACEANS 



Gammarus. — Gammarus (Fig. 130) and Hyallela (Fig. 129), 

 two of the commonest genera of amphipods in the eastern 

 states, have very similar habits. They can be found in ponds 

 and streams the year round. They mate and lay eggs from 



Fig. 130. — One of the commonest amphipods, 

 Gammarus. 



April to November, producing about 22 eggs every eleven 

 days. Embody has reckoned that a single pair of Gammarus 

 fasciatus might have 24,221 progeny in one year. This species 

 is also easy to keep for observation in an aquarium. 

 Length one inch. 



Isopods or Sow-bugs — Isopoda 



These are broad backed, flattened crustaceans which live 

 among, the bottom trash of pools. They are commonly 

 represented only by Asellus, which can be found in pools where 

 there is hardly anything else living. 



Fig. 131. — Isopod, Asellus communis: i, dorsal; 2, 

 ventral, showing egg pouch beneath the thorax. 



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