PROCEEDINGS OF THE SOCIETY. 399 



attractive, but in the immature form many of them were very remark- 

 able indeed. In the nymphal form there were some which were very 

 curious. There was a large number on the dorsal surface of which 

 two or three concentric rings would be found bordered with handsome 

 spines, or hairs changed not into spines but into scales with nervures 

 running through them almost like those of a dragon-fly's wing. How 

 these concentric rings arose was a matter of considerable interest. 

 Like almost all other Acarina, although they were eight-legged things 

 in their adult form the larva was almost always hexapod, a very re- 

 markable fact, because when the embryo was forming in the egg it 

 was clearly octopod, but it was hexapod when it emerged, and when it 

 arrived at the nymphal stage it was octopod again ; these two con- 

 ditions were at one time regarded as different species. The hexapod 

 larva being drawn upon the board, Mr. Michael showed how the process 

 of changing the skin took place, the old skin splitting all round slightly 

 under the edge, and the legs being drawn out ; the skin of the ventral 

 surface and that of the legs was dropped, whereas on the dorsal surface 

 it remained adherent, so that after going through its several changes the 

 fully grown nymph, or occasionally the adult, walked about with three 

 or four skins on its back, with a row of spines round the edge of each. 

 This was one of the most interesting points for observation. Another 

 species was then drawn on the board, showing a curious chitinous process 

 on each side of the anterior portion of the abdomen. These creatures, it 

 was explained, were vegetable feeders, having very little means of pro- 

 tecting themselves, except a hard chitinous coat, so that, if attacked by a 

 predatory insect, it would probably be seized by the leg, and its only 

 chance of avoiding capture would be to hide its legs. On the side of 

 the body there was a series of trenches like ridges and furrows, and in a 

 time of danger each leg was put into one of these trenches, and the 

 chitinous, wing-like processes of the abdomen were folded down over 

 them. This was a feature which could not be well understood unless 

 the creatures were seen alive. By means of further drawings on the 

 board, the structure of a curious pair of organs situated on the cephalo- 

 thorax, near to the abdomen, was explained. No one now doubted that 

 these were sense-organs, but at first they were thought to be stigmata 

 with protective hairs. On dissecting them out, he found that they had 

 no connection with the trachea, and it seemed probable that they were 

 organs of hearing ; the name he had given them — pseudo-stigmatic 

 organs — had been adopted all over Europe, but he did not know that 

 the investigation had been carried further. As far as he knew, they did 

 not occur outside the Acarina, and very few similar organs were known 

 outside the Oribatidse, but in the Oribatidse they were almost universal, 

 so that if they were not found upon any creature under examination, it 

 might be presumed that it was not one of the Oribatida?. 



The President thought they were very fortunate to have Mr. Michael 

 present that evening to give them these very interesting remarks upon a 

 subject on which he was an acknowledged authority. 



The thanks of the Meeting were cordially voted to Mr. Michael for 

 his communication. 



The Meeting was then adjourned to June 21st. 



