1870.] 219 [Edwards. 



them a transparent mucous sheath, which, so that it may not fix 

 them in their position, is kept in a tube form by the frustules again 

 moving over each other, and thus, as it -were, fashioning and smooth- 

 ing the inside of the tube. This sheath becomes more and more 

 dense, until it is plainly visible as forming an elongation of the tube, 

 when the frustules .again project from the end, and a new portion is 

 added. I have in this way seen a tube grow across the field of the 

 microscope, and the closely packed frustules extend themselves in 

 single file, each just overlapping those in front and behind it. The 

 membrane constituting the tube, although dense and strong, is some- 

 what elastic, but not very much so, for I have seen three or four frus- 

 tules become wedged together by one attempting to pass backwards , 

 whilst the others were moving forwards, and at such times the tube 

 does not stretch to accommodate the crowding, but yet is often bent 

 by the force of the moving frustules. In fact this force must be con- 

 siderable, as is evidenced by the size of the obstacles, as grains of 

 sand, which a small Diatom will move; and in Colletonema I have 

 seen the tough tube membrane bent inwards so as almost to collapse 

 by such a crowding as I have mentioned. 



As I have mentioned Mr. Kitton's paper in Science Gossip, I 

 must here take the opportunity of saying something in regard to that 

 article, and I feel sure that .he will not take amiss what I shall -say 

 when he understands the spirit in which it is written. 



First. I wish it to be understood that the specimens and the letter 

 accompanying them were sent to Dr. Arnott for his opinion; there- 

 after I intended to publish the facts treated of myself. However, as 

 Mr. Kitton has made public his opinions on the specimens, I will now 

 give mine ; but the fact of its being a private letter of mine from 

 which he quotes, and one never meant to be made public, must ex- 

 plain what I there say. He has considered the " queer form" to be a 

 new Fragillaria, and has named it croionensis. Evidently he does 

 not agree with that portion of my letter which he quotes, when I say: 

 " I am not in favor of naming forms after places or persons, but 

 strongly incline to distinctive and descriptive names." If the form 

 were a new species I should have named it myself; but Dr. Arnott at 

 once said it was likely to be Fragillaria capucoia var. y, and such I 

 see Mr. Roper points it out to be. in the July number of the same 

 periodical. 



As it may be of interest in connection with this point, I may say 

 that in a previous specimen of the sediment from the Croton water 



