Further Observatious on Koenenia. 



419 



In a perfectly relaxed flagellum as Dr. Hansen lias already 

 sliown, subjoiiits are seen to occur at the proximal ends of all tliose 

 joints tliat are preceeded by a Joint with smooth setae. Tliis ap- 

 pearance of the subjoint is produced by a thickened ring of chitin 

 which marks olf tliis small area from the remaining- Joint. I caunot 

 See any reason, however, for believing- that there is a further division, 

 which Dr. Hansen considers as the apical subjoint. The figure of 

 a section through the contracted flagellum as well as the other 

 figures of the flagellum in Plate 22 will show that in K. tvheeleri 

 there is no such subjoint, unless the articulating membrane be con- 

 sidered as such. The smooth setae, however, belong to the more 

 thickly chitinized wall at its line of union with this thin membrane; 

 and I have never seen, in the most contracted flagellum, that these 

 setae appear to originate as an inner ring. In more than two hundred 

 specimens each with a portion of a flagellum, the breaking never 

 oecured in the region between the smooth and the plumulose setae 

 of the same segment but always below the smooth setae in the thin 

 membrane. When the flagellum is very much contracted the thin 

 articulating portion of the wall is doubled back into the Joint, since 

 it is attached to the subjoint, which is pulled in by small muscles 

 arising from the sides of the main Joint and inserted on it. It does 

 not seem possible in the contraction of a flagellum that this thin 

 I membrane could stand the strain of a pull so hard as to double in 

 the comparatively tliick chitinous wall on which the smooth setae 

 arise. The remaining joints, which have not the proximal subjoint, 

 flare out at their proximal end after fitting into the preceeding Joint, 

 ''I which they are attached. This membranous portion of the wall 

 of the preceeding segment is attached along the line following the 

 ileast circumference of the succeeding Joint. 



It would be a waste of energy to measure any, or all of the joints 



