544 



COMPARATIVE ANATOMY 



CHAP. 



Appendage to the Race of the Arthropoda. 

 The Tardigrada, or Bear Animalcule. 



The body of these small animals, which does not exceed 1 mm. in 

 length, is cylindrical or a long oval ; it is outwardly unsegmented, and 

 carries 4 pairs of short truncated appendages armed with claws, 

 and not marked off from the body by joints. The last pair of these 

 appendages lies at the posterior end of the body. The most anterior 

 portion of the body is either narrowed like a proboscis, or marked off 



FIG. 381. Macrobiotus Hufel- 

 andii. Outlines of the body and 

 ventral chord. The supra -oeso- 

 phageal ganglion is not repre- 

 sented, ug, Infra-oesophageal gan- 

 glion ; 0!, 02, 03, 04, the 4 following 

 ganglia (after Plate). 



FIG. 382. Head of Doyerla simplex, from 

 the ventral side. The nervous system not drawn. 

 pa, Oral papillae ; mh, oral cavity ; ev, hypoder- 

 mal thickenings near the mouth (glands ?) ; z, 

 teeth; mr, oral tube; 'ph, pharynx; oe, oeso- 

 phagus ; md, mid-gut or stomach intestine ; bv, 

 hypodermal thickenings (leg glands? coxal 

 glands?) in the feet (after Plate). 



like a head. The body is covered by a probably chitinous cuticle, 

 which is thrown off from time to time (ecdysis). The mouth lies at 

 the anterior, and the anus at the posterior end of the body. In the 

 straight digestive tract which passes through the ccelome the 3 well- 

 known regions, the fore-gut, mid-gut, and hind-gut (rectum) may be 

 distinguished, The oral aperture, which is surrounded by papillae, and 

 in some cases by setae, also leads into an oral cavity, into which project 

 the pointed and sometimes calcified ends of 2 teeth. Two pear-shaped 

 or tube-like glands (salivary glands ? poison glands ?) enter the oral 

 cavity. The oral cavity is followed by a generally narrow oral tube, 

 which swells out at its posterior end into a muscular, spherical, or 

 egg-shaped oesophageal bulb (pharynx). Between the mid-gut (stomach) 



