216 MISCELLANEOUS OBJECTIONS TO THIS 



at once. In many cases the vibracula have a grooved sup» 

 port at the base, which seems to represent the fixed beak ; 

 though this support in some species is quite absent. This 

 view of the development of the vibracula, if trustworthy, is 

 interesting; for supposing that all the species provided with 

 avicularia had become extinct, no one with the most vivid 

 imagination would ever have thought that the vibracula had 

 originally existed as part of an organ, resembling a bird's 

 head, or an irregular box or hood. It is interesting to see 

 two such widely different organs developed from a common 

 origin ; and as the movable lip of the cell serves as a protec- 

 tion to the zooid, there is no difficulty in believing that al] 

 the gradations, by which the lip became converted first into 

 the lower mandible of an avicularium, and then into an 

 elongated bristle, likewise served as a protection in different 

 ways and under different circumstances. 



In the vegetable kingdom Mr. Mivart only alludes to two 

 cases, namely the structure of the flowers of orchids, and 

 the movements of climbing plants. With respect to the 

 former, he says: "The explanation of their origin is deemed 

 thoroughly unsatisfactory, — utterly insufficient to explain 

 the incipient, infinitesimal beginnings of structures which 

 are of utility only when they are considerably developed." 

 As 1 have fully treated this subject in another work, I will 

 here give only a few details on one alone of the most strik- 

 ing peculiarities of the flowers of orchids, namely, their 

 pollinia. A pollinium, when highly developed, consists of a 

 mass of pollen-grains, affixed to an elastic foot-stalk or 

 caudicle, and this to a little mass of extremely viscid matter. 

 The pollinia are by this means transported by insects from 

 one flower to the stigma of another. In some orchids there 

 is no caudicle to the pollen-masses, and the grains are merely 

 tied together by fine threads ; but as these are not confined 

 to orchids, they need not here be considered ; yet I may 

 inention that at the base of the orchidaceous series, in Cypri- 

 pedium, we can see how the threads were probably first 

 developed. In other orchids the threads cohere at one end 

 of the pollen-masses ; and this forms the first or nascent 

 trace of a caudicle. That this is the origin of the caudicle, 

 even when of considerable length and highly developed, we 

 have good evidence in the aborted pollen-grains which can 

 sometimes be detected embedded within the central and 

 solid parts* 



