TAKDIGRADA 457 



1. LINGUATULA Frolich (Pentastomum Rudolphi). Body flat, with 

 a convex back and scalloped edges; eephalothorax usually not so broad 

 as the abdomen: 4 species. 



L. taenioides (Lamarck). Body lanceolate; number of abdominal 

 rings about 90; length of female 85 mm.; width 10 mm.; length of male 

 20 mm.; width 3 mm.: the adult occurs in the frontal sinus of the dog 

 and horse and in the nasal cavities of the dog, horse, wolf, fox, goat, and 

 man; the larvae form (P. denticulatum) is 5 mm. long and 1.5 mm. wide 

 and occurs in the liver, lungs, and other organs of the cat, horse, rabbit, 

 rat, and other animals. 



2. POROCEPHALUS Humboldt (Pentastomum Rudolphi). Body cylin- 

 drical; head usually, but not always, as wide as the abdomen: 21 species. 



P. crotali Humb. (P. proboscideum Rud.) (Fig. 717). Body sub- 

 clavate; number of rings about 40; length of female 80 mm.; width 7 

 mm. ; length of male 56 mm. ; width 5 mm. : the adult occurs in the lungs 

 and body cavity of the rattlesnake and boa constrictor and a few other 

 animals; the larva (P. subcylindricus) occurs in the liver and body cavity 

 of the mouse and other small animals. 



ORDER 10. TARDIGRADA.* 



Water bears. Minute, usually aquatic animals with a cylindrical 

 unsegmented body, tapering slightly at both ends and with 4 pairs of 

 short legs, each ending with several claws, the last pair of legs being at 

 the hinder end of the body. No mouth parts are present, but a pair of 

 retractile teeth project from the mouth, beside which are the openings of 

 a pair of large salivary glands. Respiratory, excretory, and circulatory 

 organs are wanting. The digestive tract is a straight tube. The nerv- 

 ous system consists of a brain and 4 pairs of ventral ganglia; a pair of 

 eyes are usually present. The animals are hermaphroditic, the single 

 gonad opening into the cloaca ; the eggs are usually laid while the female 

 is moulting and the young develop in the empty skin. 



The tardigrads are microscopic animals which are found among 

 aquatic vegetation and at the bottom of standing water, and also in moss 

 and other damp places, where they live on both vegetal and animal food. 

 They possess the ability to exist in a desiccated condition for several 

 years. The systematic position of these animals is very obscure. They 

 are usually placed near the mites among arachnids, because of their 4 

 pairs of legs and small unsegmented body, but their simple structure, 

 primitive legs, lack of mouth parts, and unstriated muscle fibres seem to 



* See "Beitrage zur Naturgeschichte der Tardigarden," by L. H. Plate, Zool. 

 Jahrb., Abt. fur. Anat., Bd. 3, 1888. 



