THREAD-CAPSULES. 155 



Ehrenberg, Agassiz, and Owen — men whom the most 

 presumptuous would be slow to contradict, had admit- 

 ted the point without proof, because it wore so plausible 

 an air. Let me hope the reader will accuse me of no 

 immodesty in thus controverting men so eminent ; 

 he will see that whereas they have only hypothesis on 

 their side, I have the accumulated and overwhelming 

 weight of experimental evidence. 



What are these " capsules," or " urticating cells ? " 

 The uninstructed reader maybe told that all the Polypes 

 are supposed to urticate, or sting, like nettles ; and the 

 nettling organs, or urticating cells, are supposed to be 

 minute suboval microscopic capsules, quite transparent, 

 containing within them threads coiled uj), which, on 

 pressure, dart out to many times the length of the 

 capsule, into which they never return. This thread 

 Agassiz likens to a lasso thrown by the Polype to se- 

 cure its prey. I will not enter here into minute details 

 of structure, which would only confuse the reader, who, 

 if curious, will find all that is known in the works of 

 Mr Gosse, or in the treatises of Owen, Siebold, and 

 Eymer Jones. Any one who has once seen these 

 threads under the microscope darting out with light- 

 ning rapidity, especially if he uses a high power, will 

 at once admit that the hypothesis of the " netthng" or 

 "urtication'' being performed by these threads is an 

 hypothesis so obvious, an explanation so natural, that 

 — it should be doubted. In all complex matters, we 

 should mistrust the obvious explanation ; I do not say 

 that we should disregard, or reject it, but mistrust it. 



