150 THE BIOLOGY OF HYDRA : 1961 



It may be fired out as a thread is fired out; as a fly line is fired out, if 

 you will. 



HAND: Then it is not a homolog of the tube of the holotrichous 

 nematocyst such as Robson and Picken described? 



CHAPMAN: I would agree. 



HESS: I thought that it everted. Many previous investigators have 

 suggested this. 



CHAPMAN: I can't possibly imagine a tube which is many 

 many microns long and is as narrow in diameter as that tul^ule is, 

 completely everting in the sense of eversion of the capsule itself. I 

 think it's almost impossible, even for a morphologist, to suggest any- 

 thing like that. 



FAWCETT: I can, I have that kind of an imagination. 



CHAPMAN : OK, you explain it. 



FAWCETT: I am not going to explain the mechanism, but 

 direct your attention to the armament as it is folded within the 

 nematocyst. You'll agree that the armament has to turn inside out 

 in order to gain the position that it exhibits after the nematocyst 

 is fired. After firing, the part bearing the spines is smoothly continu- 

 ous with the wall of the tube and with the capsule. I think you'd 

 have a serious problem to explain it any other way. If you think 

 that only the base everts and the rest of it is flipped out like a fly- 

 rod, you would have to have a very different set of continuities 

 than you find in the fired nematocyst. I do not see how you can 

 have the base evert and the remainder flip out like a flyline. It has 

 to be one way or the other. A combination of the two mechanisms 

 is incomprehensible to me. I grant that it is difficult to visualize 

 how this entire tubule could turn inside out, but if the morphological 

 images suggest that this is true. I see no reason to doubt it simply 

 because there is no ready physical or chemical explanation. The 

 physical principals applicable to this problem may not have been 

 worked out yet. 



CHAPMAN: Yes, but the problem involved in turning the en- 

 tire tubule inside out would be tremendous. 



