ARTHROPOD A 187 



of the body is extended into a proboscis with the mouth at its 

 tip. Posterior to the proboscis on the dorsal side of the 

 cephalothorax are two pairs of eyes. All the appendages con- 

 sist of a single row of joints ; the two anterior pairs correspond 

 to the mouth parts of the Arachnida ; the third pair, sometimes 

 absent in the female, is slender and used for carrying the eggs ; 

 the remaining four pairs are very long, walking legs; thus there 



FlG. 183. Nymphon hispidium. ab, abdomen; s, proboscis; 1-7, appendages. (After 

 Hock, from Parker and Hasvvell's Text-book. ) 



are seven pairs in all. The sexes are separate and there is a 

 larval stage in the development. These animals were formerly 

 classified with the Crustacea, but it is now believed that they 

 show a closer relationship to the Arachnida. There are no 

 special organs of respiration. 



Supplementary Order Tardigrada 



The Tardigrada (Lat. tardus, slow, and gradns, walk), the 

 water bears or bear animalcules, are minute animals, not over one 

 millimeter in length, which occur chiefly in fresh water or in 

 moss, damp earth, or even along the sea shore. They have four 

 pairs of short, stumpy appendages terminating in hooks, which 

 they use for walking. The body is unsegmented and not highly 

 developed. The surface is covered with a thin, chitinous cu- 

 ticula, which is cast off from time to time, and within which the 

 eggs develop ; the sexes are separate. There are no special 



