524 Rev. T. Hincks on British Polyzoa. 



should expect them to retain signs of their descent in some 

 part of their developmental history*. 



Prof. Smitt makes no accomit of diiferences in the mode of 

 growth. Finding a species with the characteristic cell of 

 Memhranipova and the equally characteristic colonial habit 

 of Retepora'\j he at once raTds;s it as a Memhranipora. 

 But surely the remarkably diverse plan of the gemmation^ 

 which has resulted in the formation of an erect reticulate 

 zoarium instead of a continuous crust, should count for some- 

 thing. From my point of view, I should regard this form as 

 the type of a distinct genus in the Memhraniporidan series. I 

 am well aware that there will be many difficulties in seeking 

 to give practical effect to the principles I have briefly indicated ; 

 but difficulties neither few nor slight seem to attend every 

 attempt at the classification of the Polyzoa. 



To 3um up, whilst agreeing with Prof. Smitt in assigning 

 the highest systematic value to tlie zoooecium, and dissenting 

 entirely from the authors who have founded their genera on 

 mere colonial habit, I hold that the latter should not be alto- 

 gether disregarded, but that in its more marked modification?! 

 it should enter as an element into generic diagnosis. The 

 form of the zoooecial aperture, the architecture and structural 

 composition of the cell, and the plan of the gemmation are all 

 to be taken into account. I have made no reference to the 

 appendicular organs (avicularia and vibracula) as systematic 

 helps. In some sections they are very constant in character 

 and position, and may be employed with propriety as distinc- 

 tive marks ; but amongst the Memhraniporidce (Busk) they 

 constitute the most unstable and variable structural element, 

 and are of comparatively little value for systematic purposes. 



Thepolypides amongst tlie Infundibulata generally offer few 

 marked structural peculiarities. Amongst the Ctenostomata the 

 presence of a gizzard is a true generic character. The pecu- 

 liar arrangement of the tentacles in Valkeria uva of authors, 

 and some other kindred forms, on which I have founded the 

 genus Campylonema^ is a character of undoubted importance. 

 But, speaking generally, with our present knowledge we do 

 not derive much help from the polypides in constructing our 

 secondary groups. 



* Prof. Smitt himself retains the genus Flustra, Linn. ; but in an early 

 stage of gi'owth F.foUacea (and no doubt the same is the case with 

 other species ) forms a spreading crustaceous network, often of consider- 

 able size, and in this condition is not distinguishable, so far as either the 

 habit or the structure of the cell is concerned, from a Memhranipora. The 

 genus is really founded on the remarkable colonial characters of the 

 adult. 



t Memhrmiipnra sigillota, Smitt, ' Floridau Brvozos,' pirt ii. fp. 8-10. 



