INTRODUCTION. C1X 



"shell-gland," detected by Ray Lankcster* in many of 

 the Mollusca. The two organs exhibit a very similar 

 structure, and occupy a corresponding position. 



Affinities of the Polyzoa. When we come to inquire 

 into the exact position of the Polyzoa in the Animal 

 Kingdom, we encounter a host of discordant opinions. 

 They have been ranked among the Worms (Leuckart, 

 Gegenbaur, Schneider, Ehlers the two latter authors 

 placing them near the Gephyr&a] ; Barrois, though 

 doubtful, inclines to connect them with the Rotifera ; 

 Reichert would approximate them to the Coelenterates ; 

 Milne-Edwards, Agassiz, Allman, Huxley, Ray Lan- 

 kester, and others either refer them to the Mollusca, or 

 place them in a dependency of this subkingdom, the 

 Molluscoida. 



The subject must of necessity be treated briefly here ; 

 and I shall confine myself in great measure to a statement 

 of the grounds on which I hold that the Polyzoa are 

 essentially Molluscan. That they exhibit points of re- 

 semblance to the Worms may be admitted at once ; and 

 whatever view may be taken of them, this can hardly 

 excite surprise. But the question really is, to which 

 group are they united by a participation in its most 

 distinctive characteristics. Now two of the most essen- 

 tial features of the Molluscan organization are certainly 

 the gills and the foot. To take the latter first, we have 

 the equivalent of this important organ amongst the 

 Polyzoa. In one section of the class (Phylactoltemata) it 

 occurs universally. I have already pointed out that the 

 rpistome, from its position in relation to other parts, may 



* J3ee his valuable paper on "the Development of the Pond Snail, and 

 on the Early Stages of other Molluaca," Quart. Journ. Micr. So. xiv. (n. B.) 

 p. 365. 



