INTRODUCTION. CIX 



''shell-gland," detected by Ray Laiikester^ in many of 

 the Mollusca. The two organs exhibit a very similar 

 strncture, 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 Geplnjrmi) ; 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 

 MoUuscoida. 



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 eqiiivalent of this important organ amongst the 

 Polyzoa. In one section of the class [Phylactolcemata) it 

 occurs universally. I have already pointed out that the 

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



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

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

 p. 365. 



