502 G. H. PARKER 
tentacles, which are pinnate, are located one at each end of the 
mouth and three in each of its two sides. 
The autozoéids are in some respects remarkably inert. They 
may be touched, prodded, and even bent from side to side with- 
out being brought to contraction; to such treatment they respond 
like inert elastic bodies filled with fluid under slight pressure. 
Only after the most vigorous mechanical stimulation can an 
autozodid be made to respond by withdrawal. 
If they are flooded with weakly acidulated sea-water or with 
sea-water containing ethyl alcohol, they quickly contract. If 
they are touched with platinum electrodes, they give no response, 
but if a faradic current is sent through them, they draw in imme- 
diately. They contract on being touched with a naked copper 
wire, though they do not respond to contact with one that has 
been dipped in melted paraffin, showing that the reaction to the 
uncovered wire is probably due to the minute electric currents 
generated by the unprotected metal (Parker and Van Heusen, 
717). To such currents they seem to be especially sensitive. 
In withdrawing, the autozodids sink into pits in the common 
flesh of the colony. The process of withdrawal ordinarily 
involves three steps: the folding together of the tentacles, the 
sidewise bending of the zodid so that its mouth points usually 
toward the chief axis of the colony, and the retreat of the zodid 
into the zoéid-pit by a process of infolding that begins at the base 
and eventually involves the whole zodid. The folding of the 
tentacles may take place before the bending of the zodid or the 
reverse, but in either case these two operations always precede 
the slipping of the zoéid into its pit. The expansion of the auto- 
zooids is in all essential respects the reverse of their contraction 
and is brought about apparently by the slight pressure of fluids 
from within acting on relaxed tissue. 
When a single autozoéid is stimulated vigorously by a faradic 
current, it can be brought to a speedy and full withdrawal, but 
such stimulus is rarely if ever followed by the contraction of an 
adjacent zodid. When such a contraction does occur, it is by 
no means certain that it is due to the spread of an impulse from 
the stimulated zoéid, for it happens so. rarely that it may be a 
