XXVlll 
INTRODUCTION. 
power of tlie microscope, a specimen of S. nivea, wliile, by 
touching its body rudely, 1 provoked it to emit its missile 
filaments. Presently they burst out with force, not all at 
once, but some here and there, then more, and yet more, 
on the repeated contractions of the corrugating walls of the 
body. Occasionally the free extremity of a filament would 
appear, but more frequently the hight of a bent one, and 
very often I saw two, and even three, issue from the same 
cinclis. The successive contractions of the animal under 
irritation, caused the acontia already protruded to lengthen 
with each fresh impetus, the bights still streaming out in 
long loops, till perhaps the free end would be liberated, 
and it would be a loop no longer ; and sometimes a new 
thread would shoot from a cinclis, whence one or two long 
ones were stretching already ; while, as often, the new- 
comers would force open new cinclides for themselves. The 
suddenness and explosive force with which they burst out, 
appeared to indicate a resistance which was at length 
overcome : — perhaps — in part at least — due to the epithelial 
film above mentioned, or to an actual epiderm, which, 
though often ruptured, has ever, with the aptitude to heal 
common to these lowly structures, the power of quickly 
uniting again. 
It appeared to me manifest, from this and other similar 
observations, that no such arrangement exists as that whicli 
I had fancied ; — that a definite cinclis is assigned to a 
definite acontium, or pair of acontia, and that the extremity 
of the latter is guided to the former, with unerring accu- 
racy, by some internal mechanism, whenever the exercise 
of the defensive faculty is desired. What I judge to be the 
true state of the case is as follows : The acontia, fastened 
by one end to the septa or their mesenteries, lie, while 
at rest, irregularly coiled up along the narrow interseptal 
fossae. The outer walls of these fossffi are pierced with 
the cinclides. When the animal is irritated, it immediately 
contracts ; the water contained in the visceral cavity finds 
vent at these natural orifices, and the forcible currents carry 
with them the acontia, each through that cinclis whicli 
happens to lie nearest to it. The frequency with which 
a loop is forced out shows that the issue is the result of a 
merely mechanical action; which is, however, not the less 
worthy of our admiration because of the simplicity of the 
contrivance, nor the less manifestly the result of Divine 
