244 ARACHNOIDEA, 



CASE only four recognised stages of progress, besides the &%%, as proved 

 by Robin in his paper on the Dermaleichi (1868); the six-footed 

 stage, the young eight-footed stage without sexual organs, the 

 eight-footed nymph with internal but without external sexual 

 organs, and the perfect mature insect, with both internal and 

 external sexual organs. If to these we are to add two Hypopus 

 stages, and two shiftings back to Tyroglyph, as required by 

 M. Megnin's hypothesis, it complicates the matter considerably. 

 The only at all feasible way out of the difficulty is by supposing 

 that M. Dujardin and M. Megnin on the one hand, or Claparede 

 on the other, had made a mistake in the kind of species that 

 contained the other. That may be possible, and if that is the 

 only alternative offered us, men must judge for themselves whether 

 they think it more likely that M. Claparede or M. Megnin (and 

 we ought to add M. Dujardin) shall have made such an error. 

 Either will remove much of the difficulty. If it be the latter 

 who are in error, all the phenomena seem explicable on the 

 supposition of Hypopus being an internal insect parasite. If it 

 be M. Claparede, then MM. Dujardin and Megnin have got their 

 way cleared of at least one stumbling block. If neither have been 

 in error, we have the following curious succession of development. 

 I. Egg of Tyroglyphus. 2. Six-footed young stage. 3. Eight- 

 footed unsexual stage. 4. The eight-footed form seen by Claparede 

 within the preceding, and which must have been the nymph without 

 external sexual organs. 5. The Hypopus with a totally different 

 system of nutrition. The change from the preceding to this has 

 not been seen, and is yet to be proved, indeed, no connection 

 between the Hypopus at this stage and any precedent form of 

 Tyroglyphus has been shown. This has next to turn into, 6. An 

 eight-footed Tyroglyph, presumably a nymph, and, 7. Back again 

 to a Hypopus, which has been traced no further, but which must, 

 on the hypothesis of its being a phase of development, in turn 

 change into the final change (which would make the eighth), the 

 perfect insect. 



