lyo ARTHROPOD A 



should study the relations of mother and offspring for the few days 

 just after the young are detached from the mother's swimmerets. 



References on the Crayfish and the Lobster 



Chidester, F. E. 191 2. The biology of the crayfish. Amer. Nat., vol. 



46, pp. 279-293. 

 Herrick, F. H. 1911(1909). Natural History of the American Lobster. 



Bull. Bur. of Fish., vol. 29, pp. 149-408. 

 Huxley, T. H. 1880. The Crayfish. D. Appleton Co. 



Crustacea. (Entomostraca and Malacostraca.) — The Branchio- 

 poda, Ostracoda, Copepoda, and Cirripedia are certain Subclasses of 

 primitively developed Crustacea which are grouped under the 

 heading of Entomostraca as distinguished from the Malacostraca. 

 They are small in size and while not themselves especially significant 

 to man, they are of tremendous importance as the food of fishes. 



Subclass Branchiopoda. — These Crustacea generally have a shell, 

 and many pairs of leaflike swimming appendages. The Order 

 Phyllopoda includes the fairy shrimp and the brine shrimp. The 

 fairy shrhnp, Branchipus^ a most beautiful form, is found in fresh 

 water just after the ice has left certain ponds. The brine shrimps 

 Artemia salina, has been the subject of experimental work on the 

 influence of reduced and increased salinity on its characteristics. 

 One species, Artemia jertilis^ is found in the Great Salt Lake. 



To the Order Cladocera ^ belong certain species of Daphnia. 

 This form has a bivalved carapace enclosing the trunk. The eyes 

 are sessile and fused. The interesting study of phagocytosis made 

 by Metchnikoff showed that when the spores of a fungus, Mono- 

 spora, were swallowed by Daphnia^ they perforated the wall of its 

 alimentary canal, but were attacked and destroyed by the blood 

 corpuscles. (Figure 75, A and B.) Elton reports a huge multipli- 

 cation of water fleas in the Antwerp reservoirs in 1896 such that six 

 men worked night and day removing them by straining the water 

 through wire gauze. It was estimated that ten tons of water fleas 

 were taken out. 



Subclass Ostracoda. — The common bivalved form Cypris uses 

 Its antennae in swimming. It has no special economic significance, 

 except as food for other animals. 



' Banta, A. M., and associates, have made numerous important studies on sex 

 intergrades and the determination of sex in Cladocera. See his recent paper, Control 

 of sex in Cladocera, Phys. Zool., vol. 2, Jan. 1929. 



