Ixxiv INTRODUCTION. 



between the simply mamillated avicularium and the arti- 

 culated through such forms as we have in the true Mem- 

 branipora minax (Woodcut, fig. xxxi., a), in Scrupocellaria 

 ferox (Woodcut, fig. xxxi., b), and the present species. 



In Notamia we have probably the fixed form which 

 comes, on the whole, nearest to the movable " bird's 

 head," and constitutes the most direct link between 

 the two classes of avicularium (Woodcut, fig. xxxvii.). 

 Here the hollow portion (or chamber) is borne on a 

 slender stem of considerable length, from which it is 

 separated by a partition ; it expands from the base up- 

 wards ; and on the upper surface is placed the curved beak 

 ("like that of a cuttle-fish"), occupying about two thirds 

 of its length, at the base of which the mandible takes its 

 origin. The latter is much curved, and terminates above 

 in a sharp point. The upper edge of the chamber below 

 the mandible surrounds a semicircular space, closed in 

 by a membrane, which probably represents the aper- 

 ture of the normal zocecium. Two new features (both of 

 them present in the " bird's head ") make their appear- 

 ance in this form. The beak and the portion of the wall 

 of the chamber from which it rises are of horny material; 

 in the lower forms they are calcareous. Between the 

 mandible and beak, when the former is elevated, a tuft 

 of minute setae placed on a slight rising is visible, which 

 constitutes a tactile organ, and conveys the external 

 stimuli which bring the muscles into play. It is possible 

 that this structure may exist in species in which it has not 

 yet been observed ; but so far, I believe, it has only been 

 noticed amongst the higher forms (which I shall call 

 the articulated avicularia) and in Notamia *. It may, I 



* In all but HB fixed condition Notumid agrcob with the articulated group. 



