XIV INTRODUCTION. 



contracting the body and tentacles, and folding the latter 

 together. When in pursuit of food, it stretches itself 

 beyond the opening of its little dwelling, and expands its 

 wreath of milk-white arms, the starry blossom, as it were, 

 of the animal-plant. 



The calycles take the most graceful forms, resembling 

 little chalices or vases, and are often decorated with cre- 

 nated or castellated borders. In many species the aper- 

 ture is furnished with an operculum, which opens to allow 

 of the passage of the polypite, and closes on its retreat. It 

 is a simple but very effective contrivance, and exhibits 

 two or three principal modifications. In some cases the 

 margin of the calycle is cleft into a number of pieces, 

 which converge and meet in a point, and form a more or 

 less conical lid. (Woodcut, fig 19, page 178.) In others, 

 the cover is a membranous extension of the walls of the 

 calycle, which falls into plaits or folds when the polypite 

 withdraws, and so roofs over the opening. Amongst the 

 Sertulariidce, the operculum presents another and a very 

 interesting form, which has its exact parallel amongst the 

 Protozoa. It consists of a plate or valve placed within the 



Fig iv. 



\ 



calycle, a little below the orifice, which is attached to the 

 interior surface on one side and seems to be a continuation 



