i5- ELEMENTARY ZOOLOGY 



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 reach 

 maturity and produce the full number of offspring. ' ' The 

 Cyclops feed on smaller aquatic animals such as Protozoa, 

 Rotifera, etc. .They in turn serve as food for fishes; and 

 because of their immense numbers and occurrence in all 

 except the swiftest fresh waters ' ' they form the main food 

 of most of our fresh-water fishes while young. ' ! Many 

 aquatic insect larvae feed almost exclusively on them. 



Related to the Cyclops are a host of other kinds of 

 minute Crustaceans. Among these the so-called fish-lice 

 are specially interesting because of their parasitic habits 

 and greatly modified and degenerate structure. There 

 are many kinds of these parasitic crustaceans infesting 

 fishes, whales, molluscs, and worms. " As on land almost 

 every species of bird or mammal has its own parasitic 

 insects, so in the water almost every species of fish or 

 larger invertebrate has its parasitic crustaceans." Some 

 of the most common of these parasites attach themselves 

 to the gills of fishes. Here they cling, sucking the blood 

 or animal juices from the host. In form of body they do 

 not at all resemble other Crustaceans, but are strangely 

 misshapen. They are often worm-like, or sac-like, with- 

 out legs or other locomotory appendages. As with other 

 parasites (see Chapter XXX) an inactive dependent life 

 results in the atrophy and loss by degeneration of the 

 body-parts concerned with locomotion and orientation. 



Wood lice (Isopoda). TECHNICAL NOTE. Specimens of 

 wood lice, pill bugs, or damp bugs, as they are variously called, may be 

 readily found in concealed moist places, as under stones or boards on 

 damp soil. They are often common in houses, near drains or in dark, 

 damp places. Examine some live wood lice, and some dead speci- 

 mens (killed by chloroform or in an insect-killing bottle). 



