12 GEORGE BIDDER. 
including two or three of S. ciliatum. Probably in all about 
5000 living collar-cells were seen distinctly. 
Since in the existing state of our knowledge it appears to be 
inconvenient to use names for the tissues of sponges which 
connote comparison with other groups of multicellular animals, 
I shall, where useful, employ the following terms : 
Ectocyte. Any cell forming part of the external surface 
of a sponge, including the afferent system of canals. 
Mesocyte. A parenchym cell. 
Endocyte. Any cell forming part of the surface of the 
central cavity of a sponge, including the efferent system of 
canals and the flagellate chambers. 
It also appears convenient to use the term gonocyte to 
designate a generative cell. 
In this paper the “ basal width” of a collar-cell is the length 
of a line passing through four or five cells side by side, divided 
by the number of cells. The “ collar-width” is used shortly 
for the diameter of the collar at its origin from the cell. The 
“height ” of the cell does not include the collar. 
GENERAL STRUCTURE OF THE Livine CoLLAR-CELLS. 
The collar-cells of 8S. compressum in normal life measure 
about 12 high by 6°6 u extreme basal breadth (basal width) ; 
the width of the collar—the most constant dimension—being 
about 4°6. A few measurements of S. raphanus in life 
give their height 7 , basal width 5; judging from the per- 
manent preparations of L. aspera, its cells are about the same 
size as those of S. compressum.! 
1 At Plymouth, in a sponge agreeing closely in spiculation with Carter’s 
Acanthella stipitata (fide Ridley and Dendy), I have met with probably 
the smallest collar-cells yet recorded. The chambers (fig. 22) were about 
6°7 » to 83 p, the apopyle about 3°3y in diameter; the cells were greenish in 
life, about 1*7m high and ‘8 » basal diameter, appearing as a mosaic in which 
the apopyle contrasted as a large round white hole. The smallest chambers 
measured by Ridley and Dendy are three times this diameter, but Ridley 
described the structure of Acanthella pulcherrima (fide Ridley and 
Dendy) as “a transparent, almost colourless mass, . . . containing 
