242 



ARACHNOIDEA. 



CASE passes through that form in its evolution." The rationale suggested 

 for such an unusual phenomenon is, that Hypopus is a stage with 



Sketch of Tyrogflyphus mycophagus emerging from 

 Hypopus. Copied from Megnin's figure. 



a harder skin in the development of Tyroglyphus, specially 

 provided for it to compensate for its softness and aptness to be 

 dried up on the failure of moisture which, but for this provision, 

 might extinguish the race. 



The above is, we think, a statement of the facts and inferences 

 relating to this puzzling phenomenon, and the reader must form 

 his own judgment upon them. We shall only point out how 

 far M. Megnin's observations really go, where they seem to 

 correspond or differ from those of Claparede and other observers, 

 and what blanks still remain to be filled up before we have a 

 complete knowledge of the life-history of Hypopus and Tyro- 

 glyphus. 



In the first place we have mature Tyroglyphi, male and female, 

 the latter of which lay eggs. 



