572 Canon A. M. Norman — Notes on the 



long time^ but the observations on the pore-chambers are of 

 more recent date. It is Levinsen who has played the chief 

 part in their examination, and he lias pnblished figures of 

 those of many species : first in ' Videnskab-Udbytte Kanon- 

 baden "Haughs^' Togter/ 1891, pis. ii.&iii., and subsequently 

 in ' Zoologica Danica, Mosdyr,' 1894, pis. iii.-vi. Waters, in 

 some of his more recent papers, and more especially in his 

 " Observations on the Membraniporidse/^ Journ. Linn. Soc., 

 Zool. vol. xxvi. 1898, p. 654, has described and illustrated 

 pore-chambers of certain species. I have, in the following 

 paper, made much use of them in dividing the old genus 

 Membranipora, as well as in other cases. 



5. The Avicularia. 



Hincks made some use of the avicularia and vibracula in 

 the establishment of certain genera, and they have been, of 

 course, used constantly in specific characters; but these organs 

 deserve far more attention than they have hitherto received. 

 Their structure and their position in the zoarium or zooecium 

 wovild seem to constitute often most reliable aid in assigning 

 the forms to what we designate species or genera among the 

 Polyzoa, just as the presence or absence and the forms and 

 position of pedicellarise have been found of very great im- 

 portance in the classification of Echinoderma. The foregoing 

 sentence was written some months ago, and in writing it I 

 had more especially in my mind the Asteroidea. I have 

 now (March 1903) just received the beautiful Avork of 

 Th. Mortensen on the Echinoidea {' The Danish Ingolf Ex- 

 pedition,^ vol. iv. — I. Echinoidea, pt. i. 1903). The following 

 sentences are from his work, and are worthy of consideration 

 in connexion with the value of the avicularia of the Polyzoa: — 



" The characters which have hitherto chiefly been used 

 for the distinguishing between the genera and species are 

 the following : the pores, the spines, the tubercles, the 

 mouth-slits, the lining of the buccal membrane with larger 

 or smaller plates, and the calycinal area. All these structures 

 may give excellent characters, and, of course, they are always 

 to be taken into consideration. But most frequently they 

 are so relative, that it is exceedingly difHcult or impossible, 

 by means of these structures, to decide whether a specimen 

 in hand belongs to one species or another . . . By these 

 researches the pedicellarise and spicules proved to be of very 

 great systematic value; they give the most excellent characters 

 we may want. . . The padicellarKe in effect give absolutely 

 excellent systematic characters, sometimes only specific 



