. The Cambridge natural history. Zoology. 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- ti
. The Cambridge natural history. Zoology. 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 " ; 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 In the retracted state the outer portion of the vesicles is withdrawn into the basal part P (Fig. 95), so that the vesicles are then only just visible, being. Please note that these images ar
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