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 

 ring-s. 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 - 

 tube. By its side, con- 

 verging anteriorly, lie the 

 two chitinous teeth, which 



Fig. 252. — Macwbiotus 

 (Modified from Greeff. ) 



schuUzei, 



150. 



a, The six inner papillae 

 of the mouth ; h, the chitin-lined oesophagus ; 

 c, calcareous spicule ; d, muscle which moves 



the spicule; e, muscular pharynx with niasti- .,„„4-,.„il„ ^^.f,-, 



eating plates ;/, salivary glands ; ^, stomach ; may Open VCntrally mto 

 h, ovary ; i, median dorsal accessory gland ; ^|-^g mOUth - tube, aS in 

 k. diverticula of rectum. ,^ t • , i j i t 



Macrohiotus imjelandi 

 and Doyeria simj^lex, or may open directly into the oral cavity, 

 as in Ecliiniscvs, 3Iilnesium, and some species of Macrohiotus. 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 



