INTRODUCTION. 



l\\i 



order, with the exception of the highest, which occur 

 only within very narrow and definite limits. 



The raised or pedunculate character commonly assumed 

 by the hollow portion of the avicularium in this division 



Fig. xxri. Fig. mii. 



a, b, c. Fixed pedunculate avicularia. 

 d. Mamillated avicularium. 



Cellaria tenuirostris. 

 av. Avicularian cell 



becomes very pronounced in certain cases. The beak and 

 mandible are elevated on a distinct stem, and (we may 

 suppose) obtain in this way peculiar advantages for the 

 discharge of their function, whatever it may be. In such 

 forms (Woodcut, fig. xxxi., a, b) we recognize an advance 

 towards the peduncle of the true " bird's head." A 

 nearer approach to it is met with in the remarkable 

 pedunculate avicularia which occur in one or two species 

 of Membranipora* (Woodcut, fig. xxxi., c). The want of 



* .\h,,i>iratn'j;-<i *i>i,iifcra, Johnston (sec Plate XIX. fig. I, n, f>, c) and 

 .V. i-yi,Jiifnfinif, 



