230 MISCELLANEOUS OBJECTIONS TO THE 



vibracula may have been directly developed from the lips 

 of the cells, without having passed through the avicularian 

 stage; but it seems more probable that they have passed 

 through this stage, as during the early stages of the trans- 

 formation, the other parts of the cell, with the included 

 zooid, could hardly have disappeared at once. In many 

 cases the vibracula have a grooved support at the base, 

 which seems to represent the fixed beak; though this sup- 

 port in some species is quite absent. This view of the de- 

 velopment 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 imagina- 

 tion would ever have thought that the vibracula had orig- 

 inally 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 all 

 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 I 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 pol- 

 linia. 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 in- 

 sects 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 consid- 

 ered; yet I may mention that at the base of the orchida- 



