THE COLLAR-CELLS OF HETEROCGLA. 25 
The second series of changes I will call “tide changes.” 
S.compressum is a tidal sponge, and when removed from 
the water will live in a damp atmosphere for two or three days. 
The cells become rounded and transparent, they retain their 
flagella but lose their collars ; after restoring the sponge to 
healthy conditions the collars reappear. 
In some specimens gathered from bare rocks about four 
hours after the sea had left them, having been one and a half 
hours in drizzling rain, the cells were rather short, rather 
round, notably granular, and mostly without collars. The 
flagella were moving, in one sponge with greater violence than 
I have ever seen. In one cell, after ten minutes in fresh sea 
water, I thought I saw the collar reappear, but the observa- 
tion was open to doubt. 
In a sponge twenty-seven hours out of the water (in an 
empty corked bottle), the cells were very low, rounded, and 
transparent, with bright granules; the flagella were active, 
though not on all cells; collars were very rare. From the 
same sponge, after twelve hours in sea-water, another section 
showed the cells less transparent, and higher (fig. 13), with a 
few more collars; after another eighteen hours in sea-water 
there were in most parts of the sponge perfectly normal 
collared cells, in other parts the curious modification shown in 
fig. 14. Both forms of collar may be considered to have been 
regenerated, since two or three other “dry” sponges showed 
loss of collars from almost all cells, and it appears that few 
collars persist after a day’s removal from the water. 
While it is obviously impossible from these observations to 
point out with certainty the exact stimulus to which the 
changes are due, some of the facts available are worth review- 
ing. Increased salinity and retention of waste products in 
the chambers are common to the conditions producing both 
series, but the tidal changes also occurred when the salinity 
may be supposed to have been reduced. In all the suffocation 
changes the preparation had been brought to the warm tem- 
perature of the laboratory, but this was true for a much longer 
time of some sponges on which the tide phenomena were 
