Ixviii 



INTRODUCTION. 



As specialization proceeds, the chamber is minimized, 

 and the adaptive modification of the valve becomes more 

 and more varied and elaborate. In the mandible of the 

 " bird's-head " appendages it reaches its climax, whilst 

 in this form the zooecium itself has lost every trace of its 

 original character and function, and merely lodges the 

 machinery by which the curious prehensile instrument is 

 worked. 



Nowhere, perhaps, is the relation of the avicularium to 

 the normal zooecium more clearly traceable than in a 



Fig. OT. 



Membranipora longicornis, n. sp. 



c. Chamber, in which the polypide is lodged, a. Aperture, o. Operculum 

 or oral yalve. o'. Modified operculum. 



foreign species of Membranipora (as yet, I believe, unde- 

 scribed*), in which a very striking modification of the 



* I propose to name it M. longicornis, from the remarkable serrated spinet 

 with which it is furnished. 



