3° ORGANIC BEHAVIOUR 
causing it instantly to rupture ; and as soon as this happens, 
the disc is suddenly set free. The highly elastic pedicel 
then flirts the disc out of its chamber with such force that the 
whole is ejected, sometimes to a distance of two or three feet, 
Fic. 9.—Flower of Catasetum; c, column; h, horns; 7, labellum. 
bringing away with it the two pollen-masses. ‘The utility 
of so forcible an ejection is to drive the soft and viscid cushion 
of the dise against the hairy thorax of the large hymenopterous 
insects which frequent the flowers. When once attached to 
an insect, assuredly no force which the insect could exert 
would remove the disc and pedicel, but the caudicles [by which 
the pollen-masses are attached] are ruptured without much 
difficulty, and thus the balls of pollen might readily be left on 
the adhesive stigma of the female flower.” * 
Here again we have adaptive behaviour of exquisite nicety, 
and we have the transmission of an impulse very rapidly along 
the cells of the irritable horns, followed by the sudden rupture 
of a membrane. Beautiful, however, as is the adaptation, 
effective as it is to a definite biological end, the organic 
behaviour does not afford any indication of the guidance of 
* Darwin, ‘‘ Fertilization of Orchids,” 2nd edit., pp. 191, 192. 
