THE COLLAR-CELLS OF HETEROCGLA. 23 
that they have been forced into contact while of natural size, 
and then been subject to individual constriction. 
I must admit that increased optical definition proves it was 
the surface of this substance, coinciding with the upper limit 
of the basal spherules and the constriction of the cells, which I 
mistook for an intracellular septum in the “ column-and-plinth” 
cells (18). It will be shown that it is now probable that the 
form of these cells is not connected with nutrition, and that 
Dr. Dendy’s surmise with regard to them was nearer the truth 
than my own. 
Pathological Changes. 
Two distinct series of changes in form, due to abnormal 
conditions, were noticeable from their constancy of character 
and sequence. They appear interesting not only for the light 
they throw on the histology recorded in preserved sponges, but 
also from the point of view of cell-physiology. 
The first were observed in healthy living sections placed in 
a drop of sea water under the cover-slip on a glass slide; I 
shall call them “suffocation changes.’”? They consist mainly 
of the formation and elongation of a transparent neck (collum 
of authors) to the normally barrel-shaped cell. Beginning 
with increased transparency of the upper (distal) part of the 
cell, the transparent region so distinguished soon becomes 
elongated and constricted, the spherules remaining in the 
wider and opaque base (figs. 5,6, 8). Being narrower, the 
distal parts of the cells are obviously more separated than 
before. The collars become conical, expanding at the mouth— 
possibly in geometrical consequence of the constriction of the 
collum (figs. 8c, 9, 10, 11, 12). During these changes the 
flagella continue to move, so that the tissue must be consi- 
dered living; they become very gradually slower, but after all 
motion has ceased it is long before the delicate flagellum and 
collar further change their outline. The extreme form drawn 
in fig. 12 was from a section that had been under observation 
one hour and three quarters ; for another twenty minutes the 
cells were motionless, but unaltered. 
