XXV111 INTRODUCTION. 



power of the microscope, a specimen of 8. nivea, while, by 

 touching its body rudely, I provoked it to emit its missile 

 filaments. Presently they burst out Avith 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 bight of a bent one, and 

 very often I saw two, and even three, issue from the same 

 cinch's. 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 which 

 I had fancied ; — that a definite cinclis is assigned to a 

 definite aco7itium, 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 

 fossee. The outer walls of these fossas 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 which 

 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 



