INTRODUCTION. Ixxix 



on dead organisms only (as has been suggested), they 

 would certainly lead a precarious existence if dependent 

 on the chance supplies of the avicularian counuissariat. 

 The appendages, it must be remembered, have no freedom 

 of movement ; they do not go in quest of prey ; they 

 merely oscillate without variation to and fro, snapping 

 their jaws at haphazard, or when roused by some irrita- 

 tion o£ the tactile setae. Their captures must be fitful 

 and uncertain ; and if the food requires long keeping to be 

 fit for use (and under the conditions this seems to be a 

 necessary supposition), the colony must be in chronic 

 danger of a famine. If living animals be the required 

 diet, then the cilia are adequate to the supply of them, 

 and the avicularia are not. 



On the whole (though the question is certainly involved 

 in much obscurity), I am inclined to regard the avicularia 

 as charged with a defensive rather than an alimentary 

 function. They may either arrest or scare away unwel- 

 come visitors. Their vigorous movements and the snap- 

 ping of their formidable jaws may have a wholesome de- 

 terrent effect on loafing Annelids and other vagrants, 

 whilst the occasional capture of one of them may help 

 still further to protect the colony from dangerous intru- 

 sion. On this view of them, they have a function ana- 

 logous to that of the other appendage with which the 

 Cheilostomata are furnished. 



The Vibraculum, though morphologically related to the 

 zooeciura, like the avicularium, is more immediately con- 

 nected with the latter ; and we find a line of transition 

 forms linking the two together. It consists, in its more 

 perfect condition (Woodcut, fig. xli.), of a chamber, in 

 which the muscles are lodged, and a movable bristle, sus- 



