48o 



TARDIGRADA 



evaporates when desiccation takes place, and is soon replaced after 

 rain ; it forms no coagulum when reagents are added to it, and 



it probably differs but 

 little from water. Float- 

 ing in it are numerous 

 corpuscles, whose number 

 increases with age. In 

 well-fed Tardigrades the 

 corpuscles are packed 

 with food-reserves, often 

 of the same colour — green 

 or brown — as the con- 

 tents of the stomach, 

 which soon disappear 

 when the little creatures 

 are starved. 



The alimentary canal 

 begins with an oral cavity, 

 which is in many species 

 surrounded by chitinous 

 rings. The number of 

 these rings and their 

 general arrangement are 

 of systematic importance. 

 The oral cavity opens 

 behind into a fine tube 

 lined with chitin, very 

 characteristic of the 

 Tardigrada, which has 

 been termed the mouth- 



Fio. 252. — Macwbiotus schidtzei, Gr., x 150. tube. By its side Con- 

 (Modified from Greeff. ) a, The six inner papillae . . • i i- .1 



of the mouth ; b, the chitin-iined oesophagus ; vergmg anteriorly, he the 



c, calcareous spicule; d, muscle which moves twO chitinOUS teeth, which 

 the spicule ; e, muscular pharynx with masti- 

 cating plates ; /, salivary glands ; g, stomach ; may Open Ventrally mto 

 h, ovary ; i, median dorsal accessory gland ; ^jjg mOUth - tubc, aS in 

 k, diverticula 01 rectum. 



Macrohiotus hufelandi 

 and Doyeria simplex, or may open directly into the oral cavity, 

 as in Echiniscus, Milnesium, and some species of Macrobiotus. In 

 some of the last named the tips of the teeth are hardened by a 

 calcareous deposit. The hinder end of each stylet or tooth is 



