212 



MECHANICAL SYSTEM 



wall is thin and very extensible. The body of the hair, finally, consists 

 of a long row of rather thin-walled and highly turgescent cells ; at its 

 base it is expanded on its upper side so as to form a hump, which acts 

 in the same manner as the basal protuberance in the case of Biophytum. 

 As each hair is sunk in a shallow depression of the inner surface of 

 the perianth-tube, the hump soon comes into contact with the margin 



Fio. S3. 



Basal portion of an eel -trap hair from the perianth-tube of Aristolochia Clematitis. 

 A. Hair in the " normal " position. C. Hair in the " normal " position, more highly 

 magnified. B. Hair in the " locked " position. 



of the depression, if the hair is pushed upwards, and thus arrests the 

 movement very quickly (Fig. 8 3 b). 



In the " locked " position, the body of the hair stands out at right 

 angles from the surface of the perianth-tube, or is inclined slightly 

 upwards and outwards. The different hairs project on every side and 

 interlock with one another, so that the flies are effectually prevented 

 from escaping. The exit remains closed in this manner until the hairs 

 die and shrivel up ; in the course of this process of collapse the thin 

 outer walls are thrown into folds, and the cross walls approach one 

 another. The highly adaptive character of these remarkable eel- trap hairs 

 is shown, not only by the differentiation of a hinge-cell and a locking 

 device, but also by the circumstance that the inflexibility of the hair- 



