

DEVELOPMENT AND IMMATURE STAGES. 145 



may probably be regarded as a rudimentary maxillary 

 lip or hypostome ; or possibly as a tactile organ of the 

 nature of the so-called " Bauchtaster " of the Gama- 

 sidas : the earlier writers supposed that there was 

 actually no mouth- opening, but it is now known that 

 below this articulated lip, and covered by it, there is a 

 minute round hole which may probably be considered 

 to be a mouth in some, probably in all Hypopi ; but 

 there are not any trophi connected with it, and we 

 have not any reason to suppose that it is functional for 

 the purpose of taking in food. The two anterior pairs 

 of legs of de Geer's Acarus were thick and well 

 developed; but the fourth pair terminated in long 

 setae without claw or sucker, resembling in this 

 respect those of the itch-mite (Sarcopte* scabiei). De 

 Geer considered it an adult creature. 



Linnaeus in 1758* adopted de Geer's description, 

 and called the supposed species Acarus muscarum. 

 Attempts have been made to identify this with the 

 Hypopus of some particular species, but I do not think 

 that any reliance can be placed upon these efforts ; 

 neither the Linnsean description nor de Geer's afford- 

 ing sufficient detail for identification. 



E. L. Geoffrey t found what was probably either 

 the same or some allied form, and called it the " Brown 

 Fly-mite." 



Hermann J in 1757 found upon the ventral surface 

 and legs of a Scarab&us larva and of the larva of 

 Osmoderma erimita a large number of small red-brown 

 mites with short legs and spines to the tarsi ; these he 

 called Acarus spinitarsus ; his figure leaves little, if 

 any, doubt that the creature was a Hypopus, and to 

 that extent at all events allied to de Geer's Acarus. 

 Megnin and Oudemans || identify Hermann's Acarus 



* ' Syst. Nat.,' ed. 10, 1758-9, p. 617. 



f ' Histoire abregee des Insectes,' 1764, t. ii, p. 624, No. 6. 



J Memoire apterologique,' Strasbourg, 1804, p. 87, pi. vi, fig. 5. 



" Memoire stir les Hypopus," in ' J. Anat. Physiol.,' 1874, t. x, 

 p. 241. 



|| " List of Dutch Acari," part 7, in < Tijdschr. Ent.,' d. xl (1897), 

 p. 251. 



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