ENTOMOS TRA CA. 25 



or too active to escape its attack. The intestine is often filled with vegetable matter, 

 but this appears to be eaten mainly if not wholly for the sake of the animals it contains. 

 The cellulose seems to be unchanged by the intestinal juices of the animal. It not 

 only eats these minute creatures in the mass, but can single out and hunt down its 

 prey. An interesting study may be made of a Cyclops placed in a glass containing, say, 

 JParamoecia. The Copepod may hurry about, darting from spot to spot, surprising 

 its prey, or it may stealthily swim about by means of its thoracic feet, and so creep up 

 within reach of its food. For minutes together it will remain at rest, until the smaller 

 animals are collected about it, then pounces upon one and quietly devours it, and looks 

 for new prey. But it does not depend solely on hunting. It will, especially in confine- 

 ment, buiTow in decaying vegetable matter, and there seek its food ; and a decaying 

 animal is always haunted by these Crustacea, though probably more for the Protozoa 

 collected about it than for the decaying flesh itself, although that may be eaten. 



The development of Cyclops and its allies shows their primitive nature, indicated 

 also by their eye, carapax, segmentation, and appendages. They hatch from the egg, 

 as a nauplius, a tiny creature with oval, unsegmented body, a straight intestine, a 

 median eye, like that of the adult Cyclops, and three pairs of locomotor appendages 

 representing respectively the antennulas, antennae, and mandibles of the adult. This 

 larval form is of great interest because of its constant recurrence among the Crustacea. 

 No equal group in the animal kingdom combines so great diversity of form with unity 

 of fundamental structure and development as does the class of Crustacea. The 

 nauplius larva is one of the great bonds of union in the class. Barnacles, Cladocera, 

 Copepoda, prawns, and many other diverse forms have the egg at this stage, and in 

 other groups it is clearly indicated as a stage in the development of the egg. 



The changes in passing from nauplius to adult in the Cyclops are of the simplest 

 character. New segments and appendages are added to the rear of the nauplius, and 

 their front appendages are modified to serve their permanent uses. These changes are 

 effected by very numerous moultings. 



Small as the Copepoda are individually, they are of no little economic importance. 

 This importance they reach through their enormous reproductive powers. An old 

 Cyclops may produce forty or fifty eggs at once, and may give birth to eight or ten 

 broods of children, living five to six months. As the young begin to reproduce at an 

 early age, the rate of multiplication is astonishing. The descendants of one Cyclops 

 may number, in one year, nearly 4,500,000,000, or more than three times the total 

 population of the earth ; provided that all the young reached maturity, and produced 

 the full number of offspring. 



These animals thus appear in immense numbers, and their multitude compensating 

 for their small size, they are of great value as a fish-food. They form the main food 

 of most of our fresh-water fishes while young ; and some adult forms, like the Coregoni, 

 feed mainly on them. The shiners, too, which serve as food for so many larger fish, 

 derive much of their nourishment from these Crustacea. Insect Iarva3, too, find them 

 an important item in the bill of fare. 



In the sea the Copepoda are of still greater importance. Hundreds of square miles 

 of water in the Atlantic Ocean have been seen colored red by these innumerable 

 swarms. At such times the fish gather in great numbers to feed on the Crustacea ; 

 and even whales find abundant nutriment from these tiny creatures, whose numbers 

 more than make up for their minuteness. Whalers are sometimes warned of the prob- 

 able presence of their game by the appearance of these swarms of Crustacea. 



