4:16 EVENINGS AT THE MICKOSCOPE. 



stretching already; while, as often, the new-comers 

 would force open new cincUdes for themselves. The 

 suddenness and explosive foi-ce 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 rujJtured, 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 acontium, or pair of acontia / 

 and that the extremity of the latter is guided to the 

 former, with unerring accuracy, 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 fossae are pierced with 

 the cinclides. When the animal is in-itated, it imme- 

 diately 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 ad- 

 miration because of the simplicity of the contrivance, 

 nor the less manifestly the result of Divine wisdom 

 working to a given end by perfectly adequate means. 

 The ejected acontia, loaded with their deadly cnidm in 



