263 
der Theken zu gehen. Ein klemer Ueberblick soli dass erweisen.“ 
Further he says 1 ): „Aber ein Ueberblick tiber die ganze Gruppe 
lekrt den innigsten Zusammenhang aller oft anscbeinend so hetero¬ 
genen Formen unter einander; von einer Gruppe zur andern ver- 
mitteln Zwischenglieder, und diese Zwischenformen vermitteln auch 
hinsichtlich der Form und Anhéftungsweise der Deckel.“ However, 
Schneider’s apparently contradictory assertions might perhaps 
be explained in this way, that he has found my statements 
regarding the structure of the different opercula incorrect, and 
therefore has undertaken a new investigation with another result. 
He says that the large collection of Hydroids in the zoological 
museum of Vienna, which have been identified by Marktanner- 
Turneretscher has been at his disposal, and there might be 
reason to believe that by the aid of this collection he had tested 
the correetness of my investigation. But he does not seem to 
have done such a thing, and the above assertion is directly contra- 
dicted not only by my investigations, but also by the contents of 
his ovvn groups. 
The central point in Schneider’s system is that he regards 
Sertularella as the genus from which all the other genera have 
developed, but he makes no attempt to solve that question which 
in this connection should be the most important, namely, in what 
manner the different forms of opercula might have been developed 
from the operculum of Sertularella. Driesch 2 ) in the Sertulariidae 
discerns between two chief colonial types, the Diphasia- type with 
opposite and the Sertularella- type with alternate hydrothecae, and 
he has tried to show that the former type may be derived from 
the latter. From this starting point Schneider 3 ) gives the 
following sketch of the development of the different „groups” from 
Sertularella by means of a moving together of the hydrothecae: 
„Es verschwinden zunåchst eine Anzahl Gelenke aus Ursache der 
• s , ■ \ ) i x „ i - • > . j * . . ' *v. % . . i }li i ! > . , \ 
') 54, p. 521. 
2 ) 17. 
8 ) 54, p. 524. 
