DIVISION OF COLLAR-CELLS OF CALCAKEA HETEROCOELA. 129 
The Division of the Collar-Cells of the Calcarea 
Heteroecela. 
By 
31 Uriel Robertson, 3I.A. 
With Plate 19. 
Introduction. 
In 1910 Prof. Minchin and I described (5) the division of 
the collar-cells in the sponge C 1 athrina coriacea (Montagu) 
with a view to obtaining an insight into the behaviour of 
the basal granule of the flagellum during cell-division. 
In Clathrina coriacea and the Clathrinidse generally 
the nucleus lies at the base of the collar-cells, and, just 
before division, comes to the apex, which is the position it 
occupies in the embryo. In the Leu cosolenidse and most 
Heterocoela, on the other hand, the nucleus lies towards the 
apex thoughout the whole life of the sponge, and the flagellum 
arises from a granule which is only very little removed from 
the nucleus, and attached to it by a double rhizoplast. At 
Prof. Minchin' s suggestion I have recently investigated the 
division of the collar-cells of two members of the Heterocoela, 
namely, Grantia compressa and Sycon sp., 1 to see how 
the process compares in the two families. 
It was at first expected that the basal granule or ble- 
pharophast of the flagellum in Grantia and Sycon would 
lie actually in the nucleus, but that is not the case ; the 
blepharoplast in the vegetative condition of the cell is placed at 
the apical margin, and is connected with the nucleus by a 
1 Either Sycon ciliatum or S. coronatum ; it was not possible 
to determine the species, since the methods of preservation used were 
such as dissolved the spicules. 
