1 68 ARTHROPOD A 



in the water. Huxley said, "the crayfish has nothing to say to 

 himself or anyone else." 



Equilibrium. — Bunting found that young crayfish with the stato- 

 cysts removed would swim upside down as readily as right side up. 

 It is also pretty certain that older crayfish have a sense of equilib- 

 rium, although the response to rotation in their case is not definite, 

 but purely individual. 



In an experiment by Kreldl, shrimps recently moulted and lack- 

 ing statoliths were placed in filtered water and furnished iron filings 

 which they at once popped into their statocysts. By means of an 

 electromagnet he directed their movements, the animals orienting 

 according to the combined forces of the magnet and of gravity. 



Eyes. — The compound eyes have about 2,500 visual rods, called 

 ommatidia. 



Food of the Lobster and Crayfish. — Lobsters eat conchs, /^cotypus 

 (oyster drill), dead and live fish, eelgrass and My a arenaria (the long- 

 neck clam). In order to secure hard-shell clams ( Venus) they must 

 dig holes 2 feet in diameter and 6 inches deep. Crayfish are omniv- 

 orous. Some crayfish eat a great deal of vegetable matter; one 

 species, the chimney builder, Cambarus diogenes^ seeming to prefer 

 it. The vegetable matter eaten consists of dead leaves, potato, 

 onion, young corn and buckwheat. The animal food consumed by 

 the crayfish consists of worms, insects, insect larvae, a few fish, frog, 

 toad and salamander eggs, and occasionally a dead fish or frog. 

 Both lobsters and crayfish are cannibalistic. Sometimes females 

 eat eggs from their own abdomens and devour their own freed 

 offspring. 



Enemies. — The chief enemies of the lobster, besides man, are 

 the codfish, trematodes, and gregarines. The gregarine protozoan 

 Porospora gigantea is a parasite on the lobster's intestine reaching 

 a length of two-thirds of an inch. The crayfish suffers from internal 

 and external enemies. Among the plants which live with the cray- 

 fish are diatoms, bacteria and saprolegnia. Internally, Distoma 

 cerrigerum and Branchiobdella have been noted. Besides man, 

 many small animals find crayfish palatable. 



Many fish, including the black bass, Micropterus, which fisher- 

 men find very partial to crayfish, eat them. Surface reports that 

 the salamanders Cryptobranchus allegheniensis and Necturus 

 maculosus are among the chief enemies of the crayfish. Ortmann 

 mentions seeing the water snakes, Natrix sipedon and A^. lebens. 



