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ARTHUR DENDY. 
represent the shrivelled remnants of flagella, but it is ex- 
tremely doubtful. The largest collared cells of a chamber 
measure about 0‘0096 mm. in total height (including the 
collar), and the nucleus is about 00032 mm. in its largest 
diameter. 
The margins of the collars are all connected together by a 
continuous, very delicate membrane, Sollas’s membrane, which 
lies in a plane at right angles to the long axis of the collared 
cell. This membrane is seen in thin vertical sections as a 
fine thread running from collar to collar, as shown in fig. 8, 
which represents an actual preparation. If the section, how- 
ever, instead of being taken at right angles to Sollas’s mem- 
brane, happens to be taken in a plane more or less parallel to 
it, then the membrane frequently appears as an irregular 
network of delicate transparent strands, shrivelled up and 
distorted by the action of the reagents, but easily recognisable 
lying within the chamber. Fig. 7 represents such a section. 
It might perhaps be thought that if Sollas’s reticulate 
membrane exhibits its true form and relationships in vertical 
sections it ought also to do so in horizontal sections ; but this 
by no means follows, for in horizontal sections the membrane 
is severed from the collars of the cells upon which it is naturally 
supported, and being no longer kept in position by these is at 
liberty to shrivel up, which it promptly does. 
Fig. 9 is a diagram representing what I believe to be the 
natural relationships of the parts under discussion. 
From what has been said of the sizes and arrangement of 
the collared cells in each chamber it will be seen that the 
membrane uniting their margins, Sollas’s membrane, will not 
run parallel to the wall of the chamber, but will be furthest 
from it at the proximal or inhalant pole, and nearest to it at 
the distal or exhalant pole. This is actually the case, for at 
the proximal pole the membrane is widely separated from the 
wall of the chamber, while at the distal pole the two become 
confluent, as shown in the diagram, fig. 10. Hence the mem- 
brane has the form of a hollow cup, whose concavity is turned 
towards the exhalant aperture of the chamber. 
