i88 



THYSAXURA 



side, segmentally placed and opening into a connnon dnct. 

 In Muchilis there are three retort-shaped sacs on each side open- 

 ing near one another into a common duct, the vasa deferentia 

 are elongate, and are very curiously formed, being each double 

 for a considerable length, and the separated portions connected 

 at intervals by five transverse commissural ducts. 



One of the characteristic features of Insect structure is the 

 restriction of articulated legs to the thoracic region. In the 



Thysaniu-a there exist ap- 

 pendages occupying a posi- 

 tion on the hind body some- 

 what similar to that of the 

 legs on the thorax. These 

 appendages are quite small 

 bodies, and are placed at the 

 hind margins of the ventral 

 plates of the abdomen, one 

 near each side ; they are con- 

 nected lay a simple joint to 

 the sternite and are provided 

 with muscles. They are 

 found in Campodea on seg- 

 ments 2 to 7 ; in Lepisma 

 on 8 and 9, in the allied 

 Xicoletia on 2 to 9 ; in Japyx 

 1 to 7, being, how- 

 ever, more rudimentary than 



Fig. 94. — Ovaries of Thysanura : A, of Cam- 

 podea ; B, oiJapyx : C,oiMachilis. (After ^^^ 

 Grassi and Oudemans. ) 



they are in Campodea. In Machilis they attain perhaps their 

 greatest development and exist on segments 2 to 9 ; more- 

 over, in this genus such appendages occur also on the coxae of 

 the second and third pairs of thoracic legs. Oudemans thinks 

 they help to support the abdomen, and that they also assist 

 in leaping ; Grassi considers that they are supporting agents to 

 some extent, but that they are essentially tactile organs. He 

 calls them false legs " Pseiidbzampe." 



Still more remarkable and obscure in function are the vesicles 

 found near the appendages ; we figure a pair after Oudemans, 

 showing them in the exserted state. In the retracted state the 

 outer portion of the vesicles is withdrawn into the basal part P 

 (Fig. 95), so that the vesicles are then only just visible, being 



