530 Rev. T. Hincks 07i British Polyzoa. 



characterized by the presence of a jointed stem and the deve- 

 lopment of the zoooecia by budding from the intemodes of 

 this stem. For this group he suggests the name Bryozoa 

 stolonifera^ . 



I confess I cannot see that Busk's classification is inva- 

 lidated by the mere fact that we find in two or three cases 

 amongst the Cheilostomata a structure analogous to the oper- 

 cular termination of the cell in the VesiculariidcB f. We do 

 not meet with completely isolated groups ; and our zoological 

 provinces cannot be shut in by perfectly hard and fast lines. 

 In the absence of any very distinct types amongst the poly- 

 pides, the structure of the zoocecium seems to offer the best 

 systematic characters ; and the principal points selected by 

 Busk have certainly the merit of marking out very natural 

 groups, as sharply defined probably as nature permits. The 

 opercular valve of the Cheilostomata involves all the appendi- 

 cular organs {avicularia and vihracula\ which are so charac- 

 teristic a feature of this division ; the absence of operculum, 

 distinguishes the multitudinous forms which are constituted 

 by the varied combination and arrangement of simple calca- 

 reous tubes ; the setose operculum is characteristic of a very 

 homogeneous group, the VesiculariidcB ^ and also of the fleshy 

 forms included in the genus Alcyonidium. Ehlers is un- 

 doubtedly right in insisting on the marked differences between 

 these two sections in the mode in which the cell is developed 

 by budding. In the former case cells are produced only by 

 budding from a stem or stolon ; in the latter they are pro- 

 duced by gemmation from another zoooecium. 



This is an important distinction, but it seems to me less 

 significant than the structural peculiarities of the cell on which 

 the suborder Ctenostomata is founded ; and I therefore propose 

 to range these two sections under the latter as subgroups. 



Amongst the Cheilostomata the zoooecia are developed by 

 gemmation from a stolon in the ^teida^ and amongst the 

 Cyclostomata in the Crisiidce to a certain extent. 



In the genus Eucratea Ave have hoth kinds of gemmation : 

 the primary zoooecia are developed on a creeping stolon that 



• Hypoplwrella expansa, * Ein Beitrag zur Kenntniss der minirenden 

 Bryozoen,' von E. Ehlers, p. 126 (sep.), 1876. 



t In the p-enera ^tea and Eucratea the uppermost portion of the tenta- 

 cular sheath is composed of a number of delicate rods connected by an 

 attenuated membrane ; when the polypide is fulh' extended, this portion, 

 which is scalloped round the free extremity, is thrown back, and stands 

 out like a frill at right angles to the cell. This may be the homologue 

 of the setose operculum of the Ctenostomata ; but it exists in a very 

 rudimentary condition ; and as it is associated with the cheilostomatous 

 movable lip, it has lost its significance as a protective covering. 



