V. ARTHROPODE, SUMMARY OF IMPORTANT FACTS. 435 



3. The outer segmentation is expressed in the rings of the chitin- 

 ous coat of the body as well as in the metamcric arrangement of the 

 appendages. 



4. From the similarly metameric Annelida the Arthropoda are dis- 

 tinguished by the presence of jointed appendages, at most a pair to a 

 somite. The appendages may be divided according to function into 

 antennrc, jaws, accessory jaws, feet, and swimmerets. 



5. A further distinction is the grouping of the somites mto regions 

 of which usually head, thora.x, and abdomen are recognized. 



6. The head bears the tactile and eating appendages; the thorax those 

 used in locomotion (pereiopoda), the abdomen the swimmerets (pleopoda), 

 or it lacks appendages. 



7. By fusion of head and thorax a cephalothorax is produced; a 

 postabdomen may be separated from the abdomen. 



8. The eyes are either ocelli or compound eyes. 



9. Hermaphroditism is rare; reproduction is by eggs; frecjuently there 

 is parthenogenesis, rarely picdogenesis. The eggs usually have a super- 

 ficial segmentation. 



10. The Arthropoda are divided into Crustacea, Acerata, Malacopoda, 

 Insecta, and Diplopoda. 



11. The Crustacea respire by gills; they usually have two pairs of 

 antennas, and usually biramous feet; the reproductive ducts open near the 

 middle of the body. 



12. The Crustacea are divided into Trilobitse, Phyllopoda, Copepoda, 

 Ostracoda, Cirripedia, and Malacostraca. 



13. Phyllopoda, Copepoda, Ostracoda, and Cirripedia are frequently 

 called Entomostraca; they have a shell gland and the nauplius as a larval 

 stage. 



14. The Trilohitce are extinct forms with one pair of antenna3, and the 

 body divided by longitudinal grooves into three regions. 



15. The Phyllopoda have varialjle segments and primitive leaflike 

 feet recalling the parapodia of the annelids. 



16. The Copepoda are without shells and have biramous feet. 



17. The Ostracoda have reduced bodies enclosed in a bivalve shell. 



18. The Cirripedia are usually hermaphroditic and are sessile. 



19. The Malacostraca have 20 (21) segments, of which 7 (8) are 

 abdominal; the male sexual openings are on the 13th, the female on the 

 nth, segment; the excretory organ is the antennal gland; the larva is a 

 zoea, rarely a nauplius. 



20. The Malacostraca are divided into Leptostraca, Thoracostraca, 

 and Arthrostraca. 



