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XEEDHAM. 



[VOL. I. 



now clearly recognizable, all save one --the fourth segment of 

 the tarsus, whose size is small in the adult, and whose suppression 

 thus seems to extend back into the ontogeny of the species. 

 Fig. 5, B, represents a longitudinal section through the tarsus at 

 the same stage. This shows well the condition of the hypodermis 

 at the time when all is ready for that great extension which 

 accompanies pupation. Here is shown also the development of 

 the strong tendon which protracts the claw, as a hypodermal 

 imagination between segment five of the tarsus and the base of 



FIG. 6. Leg of young pupa, within the pupal skin, in part in optic section, .r, coxa ; y, tro- 

 chanter ; _/", femur: t, tibia; c, corbel; s, scrobe ; e, e, developing tendons (flexor and 

 extensor tibiae) and muscles ; /, 2, 3, 4, j, segments of the tarsus. 



the claw. At pupation this tendon is drawn out to great length, 

 the hypodermis nuclei move apart, and spend themselves com- 

 pletely in chitine formation. Thus is the tubular ingrowth of 

 soft hypoderm cells transformed into a solid cord of chitine. 

 Muscle cells developing internally at the expense of the fat are 

 from the first intimately associated with these hypoderm cells (cf. 

 Fig. 9), and through them become attached later to the tendon. 

 Just after pupation there is a striking similarity in appearance 

 between these tendons growing from the surface into the leg 

 cavity and the tracheae growing from the body cavity into it. 



