430 GENERAL BIOLOGY 



Class LINGUATULIDA ( ). Parasitic Arthro- 



poda (Pentostomidae) of worm-like build, body with metameric circular 

 muscles, two pairs of hooks in region of mouth, mouth without mandi- 

 bles. Affinities uncertain. 



Class PANTOPODA ( ). Marine Arthropoda, 



body segmented, abdomen vestigial, with not more than seven pairs of 

 legs, mouth a beak. 



Class ARACHNOIDEA ( ). Arthropods with 



either tracheae, book lungs or book gills, or both, and no antennae. Har- 

 vest-men; spiders, mites,, ticks, scorpions. 



Class MYRIAPODA ( ). Arthropods with 



distinct head, one pair antennae, breathing through tracheae, whose stig- 

 mata are placed in linear metameric arrangement, many legs. Myriapods 

 and millipeds, centipeds. 



Class MIRIENTOMATA ( ). Minute micro- 



scopic Arthropoda (600-1600 micra), with six legs, a three-segmented 

 thorax (?), no antennae, post-embryonic increase of segments, first pair 

 of legs transformed into sense .organ. These minute forms were only 

 recently discovered, and their affinity is uncertain. 



Class COLLEMBOLA ( ). Arthropods with 



6-segmented abdomen, no post-embryonic increase in segments, one- 

 jointed tarsi, few tracheae, these opening in one pair of stigmata at the 

 throat, abdomen generally with spring. Spring-tails. 



Class CAMPODEOIDEA ( ). Arthropods with 



long body, abdomen 10 segments, with cerci. No eyes, mouth-parts with- 

 drawn, no post-embryonic change in abdominal segments. Spring-tails. 



Class THYSANURA ( ). Arthropods with 



free mouth-parts and palpi, three caudal appendages, abdomen 11 seg- 

 ments and covered with silvery scales, frequently with spring beneath. 

 Silver fish, fish moths. 



Class PTERYGOGENEA ( ). Insecta, Hex- 



opoda. Winged Arthropods, with three pairs of legs, embryos with 12 

 segments to abdomen, adults with all degrees of post-embryonic reduc- 

 tion from 12 to 6 segments. Breathe through tracheae, stigmata linear 

 and metameric in arrangements. True insects i. e., winged Arthropods. 



Phylum CHORD ATA ( ). Animals having at 



some time during their life's history a notochord lying between the nerv- 

 ous system and the alimentary tract, a hollow central nervous system 

 lying entirely on one side of the digestive canal, and pharyngeal slits 

 extending from the pharynx to the exterior. 



Subphylum CEPHALOCHORDA or ADELOCHORDA 

 ( ). Fish-like chordates with a permanent noto- 



chord composed of vacuolated cells, such as Amphioxus. 



Subphylum UROCHORDATA or TUNICATA ( ). 



Sac-like marine animals with a cuticular covering known as a tunic or 



