130 



NATURAL HISTORY. 



llllcp 



contents of a little pond removed with the greatest care, so as to feel sure 

 fcha1 he bad obtained every Apus present. He obtained on this occasion 

 5796 specimens of Apus, every one of which being carefully examined 



proved to be a female." 



Firsl among the offshoots from the Phyllopods comes a group of 

 dcroscopic tonus, some species of which maybe found in every stream 



or pond, while in the sea their abundance is 

 beyond description. In their essential features 

 all are much like the Cyclops figured here, a 

 form which is perfectly familiar to every worker 

 with the microscope. For the amateurs it may 

 be well to say that no one knows what Cyclops 

 quadricornis is, and yet the name is used in 

 every text-book and microscopic manual. The 

 Cyclops and its allies have a peculiar style of 

 locomotion. They use the long antennae seen 

 projecting from the front of the body as a pair 

 of oars, taking a strong stroke, and dart quickly 

 forward, and then settle down for a few mo- 

 ments, soon to rise again and go through its 

 evolutions. 



From Cyclops a long series of forms lead 

 by insensible gradations from this free-living 

 active form to those wholly given up to para- 

 sitism. In some of the parasites the departure 

 from the normal type is but slight; one can 

 readily distinguish in them all the parts of the 

 Cyclops, and the various organs are but slightly modified. In others the 

 degeneration and consequent degradation has gone so far that in the adult 

 not the slightest crustacean feature can be recognized. All the jointed 

 appendages are gone, or are modified into organs for holding to the host 

 "i- sucking its juices; the eyes and other organs necessary for a free life 

 have disappeared, and the body has acquired a disgusting worm-like appear- 

 ance. A parasite can take life easy. It has no struggle for its food; all 

 that i< necessary is to sir still and suck the juices of its host. One would 

 think that, from the crustacean point of view, such a life would be an 

 enviable one. but it has its drawbacks. It involves a loss of personal 

 beauty, it, compels a stay-at-home life, and resolves the animal into a mere 

 machine for digestion and the formation of esrss. 



Fishes are especially affected by these parasites. They may be found 

 with these unbidden guests fastened to the jaws, hanging from the gills, 



Fi<;. 118.— Fresh-water Cyclops, 

 enlarged. 





