NO. II LEGS OF PRIMITIVE ARTHROPODS EWING 33 



In Japyx (pi. 12, %. 38) the meso- and metathoracic sternal 

 regions each is covered by a large plate which is heavily reinforced 

 by a Y-shaped apodeme. The base of this Y rests against the anterior 

 margin of the following sternal plate, and the forks pass outward to 

 articulate with the condyle of the coxa. In Japyx isahcllac, how- 

 ever, they do not stop here but extend forward to the lateral margins 

 of the plates. The prothoracic sternal region of Japyx is provided 

 with two sternal plates, and in front of these there is a neck region 

 that has already been discussed (page 26). 



In Japyx solifugus according to Borner (1903) and in Japyx jap- 

 onicus according to Enderlein (1907) and in certain other Japyx 

 species there are found posterior to the large sternal plates of the 

 pro-, and mesothorax two or three broad folds which in Japyx 

 solifugus are provided with ventral plates. These conspicuous folds 

 indicate what has been termed the intersegmental region. Verhoefif 

 believed that they represented true body segments and called the 

 mesothoracic folds the stenothorax and the metathoracic ones the 

 cryptothorax. Enderlein (1907) holds that they represent only a 

 semidetached part of the true meso-, and metathoracic segments and 

 calls them the " mesothoracical-apotom " and " metathoracical-apo- 

 tom " respectively. Crampton (1926) refers to them as " interster- 

 nites," and Snodgrass (1927) states that they belong to the sternum 

 following as " is shown by the fact that the anterior margin of the 

 first one of each thoracic set, as seen in side view, coincides with the 

 line of antecostal suture of the tergum of the same segment." 



The thoracic stigmata are situated ventrally in Japyx, although 

 this point appears to have been overlooked by most workers. Borner 

 (1903) represents the anterior pair as being situated in the membrane 

 near the posterior corners of the prothoracic sternite, while the 

 second pair is represented as being in the membrane, laterally be- 

 tween the " intersegmental folds " behind the mesosternite. In Japyx 

 isabellae (pi. 12, fig. 38) the anterior thoracic stigmata are situated 

 in the chitinous shoulderlike areas in front of the mesosternum, while 

 the second pair of thoracic stigmata are situated in a pair of diamond- 

 shaped platelets at the corners between the meso-, and metasterna. 



The trochantin (subcoxa) appears to be wanting in Japyx, but con- 

 stitutes a condyle-bearing plate in Machilis (pi. 5, fig. 13) and an un- 

 articulated crescentic plate in Campodea (pi. 6, fig. 15). In Thermo- 

 hia there is a true subcoxa, a segmentlike structure (pi. 5, fig. 14), 

 present instead of the trochantin. It has been previously discussed 

 (page 19). 



