427 



the Oribatidse he had mentioned the fact that under ordinary 

 conditions no special structure could be traced, but if the trachea 

 was saturated with moisture and then put under pressure it broke 

 up into a spiral coil. He was certainly under the impression that 

 most of the text-books described it as a spiral thickening of the 

 internal surface. 



Mr. Hilton said he had brought a slide of the trachea of 

 a silkworm, but the impression it gave him was that the spiral 

 was simply a creasing of the inside tube. He thought this could 

 be seen very plainly where the tubes branched. He thought this 

 idea of the structure was confirmed by the fact that in mounting 

 a tracheal system, when the cover-glass was pressed down, the 

 spiral appearance disappeared just as if the pressure had smoothed 

 out the creases. 



Mr. Karop could not quite agree with Mr. Michael as to the 

 description given in the text-books ; most of those which he had 

 referred to described the structure as having an external coat 

 with a spiral fibre inside it. He thought they were much obliged 

 to Mr. Merlin for bringing the subject before them. 



The President, in moving a vote of thanks to Mr. Merlin for 

 his paper, thought it had done good in drawing attention to the 

 question, and it had raised an interesting discussion; but the pro- 

 bability was that the good it had done was not equal to the good 

 it might do when the attention called to the subject had caused 

 other observers to examine the comparative structure in various 

 insects. 



The thanks of the Club were unanimously voted to Mr. Merlin 

 for his communication. 



An exhibition of photomicrographs was then given on the 

 screen by Mr. J. T. Holder, the series comprising a great variety 

 of objects — insects, plant sections, sections of animal tissues, 

 diatoms, and foraminifera, etc. — under various kinds of illumi- 

 nation, the descriptions of the foraminifera being given by 

 Mr. Earland. 



The President remarked that it was not possible to say much 

 about an exhibition like the one just given them by Mr. Holder, 

 as the subjects covered so wide a field. As far as the technique 

 was concerned he must leave it to others who were more com- 

 petent to give an opinion, but his own feeling on seeing these 

 slides was that he should like to know very much more about 



