8 INTRODUCTION. 



Thompson only treated this type of structure as of generic 

 importance, and it was reserved for Ehrenberg, 1 a few months 

 later, to use it as the basis of a new zoological group. This 

 he named the Bryozoa, and made a subdivision of his class 

 Phytozoa Polypi; his diagnosis, " Ore anoque distinctis, tubo 

 cilario perfecto" when taken in conjunction with the context, is 

 quite satisfactory. Ehrenberg, however, left the Bryozoa as 

 close allies of the Anthozoa; but later zoologists grouped them 

 with the Brachiopods and Ascidians to form the " subkingdom 

 Molluscoidea." The removal of the Ascidians to the Chordata 

 took away one of the three classes that formed this group ; and 

 the evidence for the alliance of the Bryozoa and Brachiopoda is 

 not conclusive. The two classes agree only in the presence of the 

 lophophore and the epistome, and in the absence or great reduction 

 of the pra3-oral region. The value of the evidence in these points is 

 uncertain ; for the lophophore appears to rise from a lobe in front 

 of the mouth in the Brachiopoda, and in most of the Bryozoa; 

 whereas in one group of the latter (the Entoprocta) it is a postoral 

 structure. Again, in the Entoprocta the lip-like epistome may be 

 homologous with the foot of the type of Molluscan larva, known 

 as the Trochosphere ; but in the Brachiopods and the rest of the 

 Bryozoa it is the remnant of a prse-oral lobe. 



Until these difficulties are removed it is impossible to determine 

 the exact affinities of the Bryozoa. On the one hand, the Ento- 

 procta approximate to the Mollusca; and on the other, the Ecto- 

 procta approach the Worms. 



3. THE STRUCTURE OF THE BRYOZOA. 



i 



The main facts in the anatomy of the Bryozoa may easily he 

 determined by the examination of a common form such as the 

 Hornwrack Flustra fok'acea, Linn. In this species the whole 

 Bryozoon consists of broad chitinous fronds, which expand rapidly 

 in width and branch repeatedly. The surface, when examined 

 by the naked eye, is seen to be marked by small lozenge-shaped 



1 C. G. Ehrenberg. Symbols Physicse sen Icones et Descriptiones Animalium 

 Evertebratorum, Dec. 1. Dated 1828. Text issued 1831. Fol. Polypi, a. 



