FURTHER CLASSIFICATION. 127 



cephalothorax, followed by four free thoracic segments of 

 gradually decreasing width. 



3. A tapering abdomen terminated by a pair of long, 

 bifurcated stylets. 



4. A pair of relatively large egg sacs attached to the 

 first of the four apparent abdominal segments. This first 

 segment is really composed of two segments which have 

 grown together in the development of the female, but 

 which remain distinct in the male (see cut). 



On the extreme front of the carapace find a pair of eyes 

 so close together that they appear as one under low power. 



At the front find also two long, conspicuous first an- 

 tennce, and just beneath them a pair of small second antennce. 



The remaining appendages may be seen in a ventral 

 view of the animal. They are a pair of blunt, dark- 

 colored mandibles, and two pairs of bristling maxillce, 

 surrounding the mouth, and some distance behind these 

 five pairs of thoracic appendages (legs), the fifth pair 

 rudimentary. 



Note the absence of breathing organs. Respiration 

 takes place through the skin. 1 



FURTHER CLASSIFICATION. 



We have illustrated, by examples, species, genera, fam- 

 ilies, and orders, among animals. We have said that the 

 species is the smallest zoological group, and comprises 

 animals that are essentially alike. We have combined 

 related species into a genus, related genera into a family, 

 and related families into an order. And now we have 

 extended our study far enough to have material for illus- 

 trating the higher groups. Orders are in the same way 



1 Read "Anatomy and Metamorphosis of Cyclops," in Brooks's Hand- 

 book of Invertebrate Zoology. 



