263 ! 
der Theken zu géhen. Ein kleiner Ueberblick soll dåss erweisen.” 
Further he says”): ,,Aber' ein Ueberblick iibér die ganze Gruppe 
lehrt den innigsten Zusammenhang aller oft anscheinend so hetero- 
genen Formen unter einander; .von einer Gruppe /zur. andern 'ver- 
mitteln Zwischenglieder, und diese Zwiscienformen vermitteln auch 
hinsiehtlich der Form und Anheftungsweise -der Deckel.” . However, 
Schneider's apparently contrådietory assertions might perhaps 
be explained in this way, .that- he has found my statements 
regarding the structure of 'the different opereula incorrect, and 
therefore has undertakén '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 hås been at his. disposal, and there might be 
reason' to .believe that by the aid of this collection he had tested 
the correctness 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 own groups. 
The 'central point in Schnéider'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 thé operculum of Sertulårella. Driesch>”) in the Sertulariidae 
discerns bétween two chief colonial types, the Diphasia-type with 
opposite and the Sertularella-type with alternate hydrothécae, and 
he has tried to show that.the former' type may be derived from 
the: låtter. … From this starting point Schneider?) gives the 
following sketch of the development of the different ,,groups”” from 
Sertularella by méåns of a moving together of the hydrothecae : 
»Es verschwinden zunåchst eine Anzahl Gelenke aus Ursache der 
1) 54, p. 521. 
2) 17. 
3) 54, p. 524, 
