240 



ARACHNOIDEA. 



CASE They described the species under the name of Tyroglyphus 

 ^^^' echinopus, and Claparede's name, dujardinii, must give way to 

 it; but, unhke Claparede, they found both males and females, 

 and figured them in their paper, and both are of the normal form 

 of other Tyroglyphi. It is therefore impossible that the Hypopus 

 can be the male of Tyroglyphus. 



Up to this point, however, there does not appear to be any- 

 thing in the facts observed by Claparede that is incapable, or 

 even very difficult of explanation. Hypopus is already known as 

 an external parasite on insects. May it not also be an internal 

 parasite in its earlier stage; and might not Claparbde's supposed 

 male, seen first inside the Tyroglyph, and afterwards emerging, be 

 that stage. Such a double phase of parasitism is not without pre- 

 cedent in insects. Rhipiphorus paradoxus passes its earliest stage 

 inside the grub of the wasp, then emerges while still minute, and, 

 fastening on its outside, finishes off its victim. Subsequent dis 

 coveries, however, have introduced new and surprising elements, 

 apparently inconsistent with such an explanation. In 1873, M. 

 Megnin (first in the " Comptes Rendus," and then in M. Robin's 

 " Journ. Anat. Phys.'O, published the results of a long continued 

 and careful observation, undertaken to solve the true relations of 

 the Hypopi and Tyroglyphs, taking for his subject another Tyro- 

 glyph (which he named Tyroglyphus rostroserratus), which was 

 very plentiful in the common mushroom (Agaricus campestris), and 

 very destructive to the mushroom cultivation around Paris ; and 

 in 1874 he published, in the same work, further researches on it 

 and another mushroom-feeding species (which he named T. my- 

 ceticola). The importance attached to his researches may be 

 judged from the fact, that for them he received from the Academie 

 des Sciences the Thore prize of 1873. He placed his specimens 

 in cages specially provided for them, supplying them with shreds 

 of mushrooms which served both as food and lodging for them. 

 In observing these, one of the first facts that struck M. Megnin 

 was, that so long as the mushrooms were moist and. in full decom- 



