DEVELOPMENT AND IMMATURE STAGES. 167 



attention to it, I was inclined to regard them as adult. 

 But we know so little of their life-histories that it is 

 doubtful whether there is any other nymphal stage 

 than that supposed to be hypopial ; no other nymph is 

 known ; if there be not any then the creature which is 

 known may be the ordinary nymph, not the hypopial. 

 Undoubtedly its habits seem more consonant with 

 the hypopial hypothesis, as the known species are 

 parasitic, when in this condition, upon wild bees of the 

 genera Osmia, Xylocopa, etc., and can endure the 

 exposure to heat and drought which this involves. 

 Moreover they are provided with suckers on the 

 ventral surface for adhesion to the host, as Hypopi of 

 the ordinary type are ; but, on the other hand, they 

 are not enclosed in a smooth chitinous carapace like 

 other Hypopi; but have a softer, although tough, 

 cuticle; usually wrinkled, and they have immense 

 single claws on the first three pairs of legs ; apparently 

 for adhesion, which are not usually found on other 

 Hypopi. Moreover, they have more indications of 

 mouth-organs than other Hypopi have ; although these 

 parts must still be regarded as rudimentary. Per- 

 sonally I am inclined to look upon these nymphs as 

 hypopial, but I do not think that it can be said to be 

 finally proved. 



Dufour first described one of this form of Hypopus in 

 1839.* He found it upon Osmia bicornis and O.fronti- 

 cornis ; he looked upon it as adult, and called it Tricho- 

 dacti/lus osmide. Donnadieu subsequently found another 

 upon Xylocopa violacea, and called it Triclwdactylus xijlo- 

 cop33.-\ Berlese J subsequently traced the adult of the 

 latter form. Canestrini has added two other forms from 

 New Guinea. Donnadieu regarded the creatures as 

 adult, and describes mouth-organs, including maxillas ; 

 which he admits are anchylosed and fixed, and only 



* In ' Ann. Sci. Nat.,' 2e ser., t. ii, p. 267. 



} " Recherches anatoiniques et zoologiques sur le genre Tricho- 

 dactyle," in ' Ann. Sci. Nat.,' ser. 5, t. 10, pp. 6985. 

 | 1885, Berlese, ' A. M. S.,' fasc. 18, No. 1. 

 In ' Term. Fiizetek,' v. 20, 1897, p. 474, v. 21, 1898, p. 176. 



