208 INTERNAL ANATOMY. 



also was unable to find any special respiratory 

 organs in MachUis} Yet, though the tracheae 

 are not largely developed in the Thysanura, in fresh 

 specimens of Lejpisma they are easy to see. In Gamjpo- 

 dea, according to Meinert, the spiracles are six in 

 number, two for each of the thoracic rings. The 

 prothoracic spiracles are the largest, and are situated 

 on the underside, at the posterior margin of the pro- 

 sternum. The two other pairs, on the contrary, are 

 situated on the upper side, behind the dorsal shields of 

 the second and third thoracic segments. In this 

 genus there are no abdominal spiracles. 



In lapyx, on the contrary, there are ten pairs of 

 spiracles, " situated in the side folds of the first ten 

 rings. 



The nervous system consists of a supraoesophegeal 

 and eleven suboesophageal ganglia. 



The digestive canal is a straight tube. In Lepismo? 

 it consists of a pharynx, an oesophagus which gradu- 

 ally enlarges so as to form a first stomach, a crop, ^dth 

 six horny teeth, a true or second stomach, a narrow 

 ilium, and a somewhat wider rectum or colon. The 

 Malpighian vessels are four in number and filiform, 

 situated in front of the ilium. In Cariipodea, on the 

 contrary, there are no Malpighian vessels, but the 

 hinder end of the stomach, which Meinert calls the 

 duodenum, is surrounded by a circle of about sixteen 

 rather large glandular cells. In laj^yx the intestinal 

 canal consists of an oesophagus, a large cylindrical 

 stomach, and a short intestine ; there is no distinct 

 crop, nor are there any Malpighian vessels. 



In lapyx the ovaries consist of two wide tubes, 

 opening at the posterior end of the eighth segment. 

 In Campodea, again, both the ovaries and testes consist 

 of long, simple, wide tubes, one on each side, and 

 opening also at the posterior end of the eighth segment. 



' ' Nouv. Anu. d. Museum,' vol. i. 

 - Meinert, 'Ann. Mag. Nat. Hist.,' 1867, p. 371. 



3 Treviranus, ' Yer. Schr.,' vol. ii, p. 13. Ramdohr. Verd. "Werk. d. 

 Ins.,' p. 150. 



