208 NATURAL HISTORY OP 



in all cases the spermatozoa and ova are developed 

 upon it. Budding also, or the growth of a colony by 

 gemmation, proceeds from the endosarc. 



The function of the funiculus would therefore appear 

 to be reproductive and not nervous. 



In many species of the Cheilostomata the zooecia are 

 protected by avicularia or " bird's-head processes/' 

 and in a few species by vihracula or "bristles." 



The avicularia differ in shape very much, varying 

 from slightly differentiated zooecia to elaborate struc- 

 tures like those of the BugultB (Plate XVI., fig. 7). 

 This structure is one which — viewed in anyone species 

 without consideration of others — would cause consider- 

 able difficulty in deciding as to its nature, but when 

 the avicularia are considered as they occur throughout 

 the Cheilostomata, it is found that a development of 

 form can be clearly traced, which shows that the 

 avicularia were originally modified ordinary zooecia, 

 and that, through a multitude of gradations, they have 

 passed in some species into highly specialized organs. 

 Mr. Hincks has very elaborately advocated this view 

 in his '' British Marine Polyzoa,'' and in the Annals 

 and Mag. of Nat. Histoiy, vol. ix. page 20. 



The avicularia are supplied with muscles to regulate 

 their movements, and in some of them is found a 

 cellular body, considered by Mr. Hincks and others to 

 be the analogue of the polypide. It is often armed 

 with bristles, and, therefore, probably serves for tactile 

 purposes. 



The use of these curious structures is much ques- 

 tioned. Some have regarded them as food providers, 

 and they have been observed to hold small woi'ms, &c, ; 

 but as they are not always placed in positions where 



