259 
proximal part of all the branches the hydrothecae are arranged. in 
three longitudinal series, and in one of them this arrangement is 
continued through its whole length while in the others the rest 
of the hydrothecae are biserial. In another Thujaria-species, de- 
scribed by Torrey?") under the name of Sertularia incongrua the 
branches in their proximal portion possess two series of hydrothecae, 
and usually three series in their distal half. Nutting refers this 
species to Selaginopsis triserialis Mer.; but according to Meresch- 
kowsky the triserial arrangement of the hydrothecae is im the 
latter species constant through the whole colony. Lastly I shall 
mention that Bale?) in a våriety of Sertularia unguiculata Busk 
has found in -some of the pinnae 'fa third series of hydrothecae, 
running for some distance along the front of the first internode.” 
The fact that there is no constant relation between the 
structure of the zooids and the colonial form, or to express it in 
another way, that they are incommensurable values defined by 
different laws, must have the logical sequence that one of them can- 
not be substituted for the other, and, therefore, a genus ought never 
to be instituted solely on the base of a difference in the colonial 
form, when otherwise the zooids present distinct structural diver- 
sities. When. that is not the case, as in the great plurality of 
the cyclostomatous Bryozoa, we have of course only the colonial 
form to rely upon. To regard the colonial characters as the true 
generic characters and the zooidal characters only as specific cha- 
råcters, as some authors have done, is to turn the systematic 
arrangement upside down. — 
In 1897 Dr. C. Sehneider?) published a paper on the 
Hydroid polyps from Rovigno?), in which, besides, he sets forth 
a number of systematic remarks, of which we shall here only 
mention those referring to the Sertulariidae. 1 may give here 
n) 57, Pp. 69. i z i ; j i ; i e 
3 40 
3) 54, 
