23S 



ARACHNOIDEA. 



CASE with a form of Parthenogensis, which we otherwise know does 

 occur among Acarids. In the course of this examination a Hy- 

 popus, which continually appeared with Tyroglyphus, attracted 

 his attention, by means of which he hoped to establish Dujardin's 

 hypothesis. But he never succeeded in doing so. He found a 

 Hypopus in the act of metamorphosis, and thereby satisfied him- 

 self that it could have no possible relation with Gamasus ; and 

 he speaks with confidence, because for three years he brought up 

 Tyroglyphi and Hypopi from hyacinth bulbs in his work-room 

 without ever a single Gamasus making its appearance from or in 

 connection with the others. The Hypopi were in thousands, but 

 they were all of the same size; and the young stage, or individuals 

 in the act of transformation, were not to be found. Neither did 

 he observe any difference of sex, as all examples resembled one 

 another throughout. Nor could any individuals with eggs be 

 found. The manner of increase of the Hypopus thus appeared 

 in the highest degree enigmatical, the more so that the extreme 

 stiffness of the mail-like skin renders the idea of growth after it 

 has acquired it inadmissible. The conclusion forced itself upon 



Young larva of Rhiz'-glyphus echinatiis 



(Tyrog-lyphus dujardinii, Clap.), the 



posterior leg's not visible from above. 



Copied from Claparfede's figure. 



Young- stage of Tyroglyphus develo 

 inside of Tyrog-lyplius dujardinii. 

 Copied from Claparcde. 



him, that the young stage of the Hypopus must be sought for 

 under quite another form. It next occurred to him that he might 

 succeed better by following the development of the Tyroglyphus 

 from the beginning through its various stages. This he did, and 

 first he found the six-footed larva proceed from the ^gg, bearing, 



