253 
character. Electra pilosa lends strong support to this view. Yet 
it is a view nevertheless in which I am not prepared in all cases 
to acquiesce. The zooecial characters are unquestionably all im- 
portant, but no lasting classification can be based on any part of 
the zooecium....: Why also in all instances is the ultimate 
growth and form of the zoarium to be excluded from generie cha- 
racter among certain families of the Cheilostomata, and at the same 
time to be recognized among the Cyclostomata and Ctenostomata, 
and even other groups of the Cheilostomata? This is surely 
scarcely consistent. In some instances, as for example in Electra 
pilosa, the form of the colony.is of no generic and specific value, 
but in other cases it may be and, I believe, is.” 
In the systematic arrangement of most families of Hydroids 
the chief stress has not as in the earlier Bryozoan system been 
laid on the colonial form, but partly on the structure of the zooids 
partly on the different mode of reproduction, and the differences 
of opinion have arisen mostly from the question how great systematic 
importance ougth to be ascribed to the latter. The reason hereof 
is partly, that the zooids which are much larger and therefore 
much easier to examine than those of the Bryozoa, present a 
number of easily recognisåble characters, f. inst. in the different 
form and arrangement of their tentacles, and in the different form 
of their proboscis and hydrothecae, partly, that the colonial form in 
most families does not present such differences which might tempt 
a systematist to the institution of genera. Such are on the con- 
trary to be found in the Sertulariidae, in which the mode of 
arrangement of the hydrothecae together with the mode of branching 
is subject to very great variation, and, therefore, to a great extent 
has been used by the systematists. Ås soon as the operculum 
was detected and used as a systematic character there began a 
discussion about its systematie significance which stili continues. 
The first author who recognizes the systematic importance of 
this structure was HincksY. While Grey had characterized 
rer 
