TYPE ARAGHNIDA. 



467 



developed system of muscle-bands. There are no special 

 organs either for respiration or circulation. 



The mouth, surrounded by papillae (Fig. 214, p), lies at the 

 anterior extremity of the body, and leads into a tubular 

 mouth-cavity containing, imbedded in 

 its walls, a pair of chitinous or partly 

 calcareous teeth, and receiving the 

 ducts of two glands {sg) which have 

 been regarded as salivary or perhaps 

 poisonous in function. Behind, this 

 cavity opens into a muscular pharynx 

 (pA) which is connected by a short 

 oesophagus with the mid-gut. At the 

 Junction of this with the rectum or 

 hind-gut is a pair of csecal diverticula 

 (Ig), probably Malpighian tubules, and 

 into the hind-gut there also open the 

 ducts of the reproductive organs, the 

 hind-gut thus serving as a cloaca. It 

 opens on the ventral surface of the 

 body a short distance from the pos- 

 terior extremity and therefore in front 

 of the last pair of appendages. 



The nervous system consists of a 

 supraoesophageal ganglion (ce) united 

 with a chain of four pairs of ventral 

 ganglia. No special sense-organs occur 

 except two eyes situated at the sides 

 of the head. The sexes are distinct, 

 the reproductive organ being unpaired 

 and opening into the cloaca, into which 

 opens also in both sexes an unpaired 

 accessory gland. 



The Tardigrada occur in water usually, especially in such 

 locations as the gutters on the roofs of houses, though some- 

 times found also among moss. The group contains but a 

 small number of genera, of which Macrobiotus is perhaps the 

 most common. 



Fig. 214. — Diagram of 

 Structure of Macro- 

 biotus Hufelandii (com- 

 bination of figures by 

 Plate). 

 an = anus. 



ce = cerebral ganglion. 

 dg = dorsal gland. 

 Ig = lateral gland or Mal- 

 pighian tubule. 

 m = muscle. 

 ov = ovary. 

 p = papillae. 

 ph = pharynx. 

 sg = salivary(?) glands. 



