Royal Microscopical Society. - 3 



or less distinctly, but the cast skins and the specimens in an early 

 stage of the j^rocess have shrivelled ujd beyond the most scanty 

 recognition. 



I did not then call attention to the curious incident, beyond ex- 

 hibiting the slides at one of the Wednesday evening conversational 

 meetings of this Society, and it had nearly passed from my memory 

 till I read a short paper by Mr. Tatem, in the ' Monthly Micro- 

 scopical Journal,' on some new Acarelh. In that paper two species 

 are figured, and described as A. Muscm and A. Pulicis : the former 

 strongly calling to my mind Topping's " rare " parasite of the house- 

 fly, and the Hypopus of the ' Micrographic Dictionary,' while the 

 other, which Mr. Tatem says he found in a dead flea, is, I believe, 

 the same species which I detected in the act of ecdysis, recorded here, 

 and which I am well acquainted with, as parasitic upon various 

 arachnida. As Mr. Tatem says his figures were from the balsam 

 preparations, I could at once understand why the curious rostrum 

 is omitted, and the two hind pairs of legs are figured as they are in 

 the illustration. Had Mr. Tatem seen them in the living state 

 under the microscope suitably illuminated, I feel sure his figures 

 would have been difierent, and he would have modified what he 

 says in the first paragraph of his communication. For certain all 

 the legs are free, and the statement that the two posterior pairs are 

 " neatly packed up in their trunks ready for evolution in the pro- 

 gress of growth " is not correct. The Hypopus, or Acavellus, walks 

 upon all its eight legs. The two posterior pairs are very short, but 

 each of them is furnished with a very long and delicate bristle 

 (only seen well in life), which materially assists the creature in its 

 small powers of locomotion.* 



With regard to the other important statement about their " ob- 

 viously imperfect development," I must also venture to difi'er from 

 him, from the incident I have above recorded. 



I communicated with Mr. Tatem on the subject, and forwarded 

 him slides containing specimens, some of which he recognized as 

 very like his own Acarellus, and others were not so conclusive. I 

 also sent him cork cells containing living examples of the Acarellus 

 in question, and its suspected earlier stages, but ill-health at the 

 time prevented his giving the necessary attention to the subject, 

 and so he returned me the cells with the request that I should 

 pursue the inquiry, courteously admitting (if my recollection is 

 correct) that there was the possibility of a mistake in his conclu- 

 sions, as the data he had to go upon were so scanty, and the balsam 

 preparations and previous liquor potasste treatment might have 

 obliterated the view of certain important points. I have to thank 



* This statement has refei-ence more particularly to my supposed Hupopua 

 (or Aciirllns) Mxisccc. The other Hypopus has shorter legs, terminating ia 

 single claws. 



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