THE COLLAR-CELLS OF HETEROCGLA. 91 
appearances are consonant with the flagellum being a rod-like 
or tube-like process of the nuclear sheath. 
Vosmaer (19, fig. 8), figures, without describing, such a con- 
nection in Halichondria; and Heider (7), in the larva of 
Oscarella, describes the root of the flagellum at the nucleus. 
With this structural disposition may be correlated the general 
(not invariable) distal position of the nucleus in collar-cells 
that are elongated, as shown for Heterocela by myself 
(18, fig. 4) and Dendy (20, fig. 24). Leucosolenia is figured 
by Minchin (17, figs. 2 and 3) and myself (18, fig. 3) with a 
distal vacuole to each cell and a basal nucleus; Spongilla, 
according to Vosmaer’s plate, differs in these respects from 
Halichondria precisely as Leucosolenia from the Hete- 
rocela. A suggestion has been made to me that the nucleus 
serves the flagellum as a mechanical fulcrum in the semi-fluid 
protoplasm ; and it is obvious that if the whole intra-choanal 
area be a cell-mouth the flagellum can have no permanent base 
except in the interior of the cell. If this view be correct, the 
same function would seem to be performed in certain lines of 
descent by the walls of a permanent vacuole, verifying for 
Leucosoleuia an alternative suggestion of Minchin’s (1.c.), 
who doubted “whether this space represents a ‘ Central- 
k6rper,’ or a kind of food-vacuole, or whether it is in some way 
connected with the movements of the flagellum and collar.” ! 
Maas’s embryological work on Silicea (21) seemed to point to 
the possibility that the relative size of nuclei might indicate 
'T have no intention to discuss the classical literature on connections 
described in other groups between nuclei and flagella on cilia. But my 
friend Mr. J. J. Lister has kindly pointed out to me the description of 
Camptonema nutans (a Heliozoon-like organism) by Schaudinn (25) in 
which he describes the axis of each pseudopodium expanding to envelope a 
nucleus in a manner most suggestively recalling the condition drawn in my 
woodcut at ¢. Schaudinn puts forward tentatively the view “‘ dass der Kern 
bei der Bewegung der Pseudopodien eine bedeutende Rolle, vielleicht als 
regulatorisches Centrum, spielt.” I think we should first carefully test on 
Leucosolenia and Spongilla the hypothesis I have borrowed above before 
yielding to the ever-enticing temptation to appeal to the nucleus as cell- 
brain, 
