398 



ARTHROPODA 



Tardigrada. 



These are minute fresh-water forms, known to microscopists as 'water bears' 

 (fig. 433), which owe their name to their slow motions. They have four pairs of 

 short, hooked legs, their sole Arachnidan character. The genital ducts empty 



FIG. 432. FIG. 433. 



FIG. 432. Larva of Pentastomum proboscideum (after Stiles), d, stomach; e, gland 

 cells; m, mouth; st, stylet; y, posterior larval hooks; i, 2, legs 



FIG. 433. Macrobiotics hufelandi, water bear (after drawings by G reef and Plate). 

 I-IV, legs; d, accessory glands; m, stomach; mk, mouth capsule; ov, ovary; sp, salivary 

 glands; st, stylets; vm, excretory tubules; blood cells in the body. 



FIG. 434. Nymphon strcemii* (orig.). c, cheliceras; o, ovigerous legs; p, pedipalpi; 



r, rostrum. 



into the rectum; the nervous system has four ventral ganglia; heart and respira- 

 tory organs are lacking. In development they are remarkable for the large 

 ccelomic pouches. In the feet are glands recalling nephridia in their history. 

 It is possible that these animals are to be placed among the Ccelhelminthes. 

 Macrobiotus.* 



