2 Transactions of the 



these legs took up and the refractive character of the medium 

 rendered them nearly undiscoverable, and in this state I after- 

 wards recognized one of them as the Hypopus of the ' Micrographic 

 Dictionary,' and as identical with Topping's preparation of the 

 Parasite of a House-Fly,* which he always designates as " rare." 

 I read the description in the ' Micrographic Dictionary,' under the 

 heading Hypopus, and had no reason at that time to question the 

 suggestion of Dujardin there alluded to, about the origin of these 

 said Hypopi. In my article in ' Science Gossip' for 1869, p. 243, 

 on Pseudo-scorpions, I mentioned both these parasites, and fur- 

 nished rough figures of them, but owing to some misunderstanding 

 only one of the illustrations was inserted ; the other was omitted 

 from the paper altogether. 



About this time also I noticed tliat my cells were infested with 

 another acarus.j very like a cheese-mite, but distinguishable on 

 account of its dirtier appearance, especially in its earlier stages. A 

 group of half a dozen of them would be seen devouring the decaying 

 malt and other substances — in fact, wallowing in the filthy mess 

 they made like so many tiny pigs ; and in some cells all the corners 

 where the pabulum of the Podurae or their excrement had accumu- 

 lated were occupied by similar groups of these disagreeable-looking 

 acari. I desired greatly to expel the dirty intruders, but as it generally 

 happened after making a collection of Podurae, &c., that a few fresh 

 ones were inadvertently introduced, I concluded that the task was 

 hopeless, for the reason that they swarmed in the earth equally with 

 the Hypopi previously mentioned; and so I paid them no more 

 attention. 



Two years ago, however, in the month of September, I picked 

 up a decayed potato, which had such a large population of these 

 acari upon it that I was induced to give it some close scrutiny, 

 chiefly with the view to satisfy myself whether these mites were the 

 so-called " cheese-mites " (Acarus domesticus) or another species. I 

 soon saw that there was a remarkable change going on in the case 

 of the greater number of them. They were casting their skins ; 

 and when this operation was complete they had metamorphosed 

 into my other little friends, the Hypopi.$ So curious an incident 

 prompted me at once to sweep ofl* all the acari into benzole and 

 mount them in balsam. For some weeks afterwards the slides thus 

 made showed the interrupted stages of the process of ecdysis very 

 well, but time has altered all that now. The slides (or rather, the 

 only one I have left at the present time) exhibits the Hypopi more 



* I speak from memory only, and may be wrong ; anyhow it is a very closely- 

 allied species. 



t I have since come to the conclusion that these also may be distinguished 

 as two species, one of them much more like a cheese-mite than the other. 



J I am disposed to consider this Hypopus identical with Mr. Tatem'a 

 Acarellus Pulicis, to be referred to presently." 



