I. CRUSTACEA: COPEPODA 369 



basal joints of the maxillae (fig. 374, 71') can be used in eating. Two maxillipeds 

 (formerly regarded as the separated branches of an appendage) mark the 

 termination of the head (fig. 385, 5). 



The internal anatomy is simple. There is no liver, and the straight 

 intestine (fig. 385) runs without marked changes in size to the anus 

 between the branches of the furca. The visual organ is the unpaired 

 nauplius eye (which has given the name to one genus, Cyclops). It lies 

 directly on the brain. The ventral chain has its ganglia irregularly dis- 

 tributed. Gills are always absent, as are usually the heart and blood- 

 vessels. The gonads are unpaired, but the sexual ducts, which open at 

 the base of the abdomen, are paired. The females possess a receptaculum 

 seminis distinct from the oviducts, to which the male attaches spermato- 

 phores packed with sperm (fig. 385, sp). As the eggs leave the oviduct 

 they are fertilized by the sperm issuing from the spermatophores, and 

 are enclosed in a gelatinous substance, thus producing the so-called egg- 

 sacs, attached to the abdomen, by which one can easily recognize the 

 females (fig. 7). A nauplius hatches from the egg, and by budding seg- 

 ments and appendages at the hinder end, and by a change of the nauplius 

 appendages into antennas and mandibles, passes through a ' cyclops-stage ' 

 into the adult. The Copepoda have descended from some phyllopod- 

 like form. The poorly developed ventral chain, the loss, partial or com- 

 plete, of a circulatory system, and the absence of gills are all against the 

 view which would consider them primitive. 



Order I. Eucopepoda. 



The forms to which the foregoing description will apply are the Eucopepoda, 

 and include many species, which often occur in enormous numbers in both fresh 

 and salt water, forming the larger proportion of the plankton. They thus 

 furnish the most important food supply not only for fishes but for the giant 

 baleen whales. Celochilus septentrionalis occurs at times in such myriads that 

 the sea for long distances is colored red. 



The CvcxopiDyE, no heart and paired egg sacs, fresh-water; Cyclops* (fig. 

 7). CALANID/E, fresh water and marine; heart present, single egg-sac. Diap- 

 tomus* fresh water (fig. 385); Cetochilus* Pontilla* marine. HARPACTID^E, 

 creeping forms, mostly marine; Canthocamptus* fresh water. The CORYC.^ID.E, 

 half parasitic, include the wonderfully iridescent Sappliirhia* and the XOTODEL- 

 PHID.E, parasitic in ascidians, form a transition to the next order. 



Order II. Siphonostomata (Parasita). 



There are aiso Copepoda to which the account in large type will not apply, 

 animals of such strange appearance that many of them were long regarded as 

 parasitic worms (figs. 6, 386, 388). Their mandibles are altered to piercing 

 bristles and enclosed in a piercing proboscis formed of upper and lower lips. 

 With this sucking organ they bore into the skin or gills of fishes. They have 

 cylindrical forms or bodies of the most bizarre shapes, in which frequently no 

 24 



