Eleventh Eeport of the State Entomologist 257 



was kept tightly corked. The mites did not take kindly to this substance 

 as food. Nine months later the vial was examined and one well de- 

 veloped smaller Hypopus was found, with the other two in a partly 

 transformed condition. 



Thus my observations appear to show that there are the larger mites 

 presumably males and females (two of them were observed apparently- 

 pairing), the immature and two Hypopal forms to be found in this species. 



The Hypopus. 



This form has long been a puzzle to naturalists. It was observed by 

 DeGeer as early as 1735 in great numbers on the house fly. It was 

 given the name of Acaius muscanuu. Similar mites were also found later 

 by others on different insects. Much later, in 1834, Duges transferred 

 the Acarus viitscarum to the genus Hypopus, which he established for a 

 mite found on Bister. The Hypopi are found abundantly at times 

 attached to the chitinous body walls of different insects, and some are 

 even found upon polished fern leaves and other hard surfaces, — places 

 where they could obtain no nourishment. They are attached by means 

 of their vemral suckers wath their anterior feet in the air, or, as m the 

 species studied, they may fix themselves by the suckers upon the feet. 

 Later studies of the Hypopus reveal other species. In these studies, M, 

 Dujardin noticed some that were narrower, more transparent, and com- 

 pletely empty; some of these, but more rarely, showed in the interior 

 another form of mite, soft and curled up like an embryo ; it occupied the 

 whole internal cavity of the Hypopus as if the latter were a living egg- 

 shell provided with feet. From this he derived the conclusion that the 

 Hypopi were larvae or rather, "if the phrase were allowable, eggs fur- 

 nished with feet." 



In 1868, M. Claparede announced as the result of his researches that 

 the genus then known as Hypopus was but the male form of certain 

 Tyroglyphidae. He traced the development of the mite from the egg, 

 and found that it emerged as a six-footed larva, thus disproving the 

 interpretation of this form by M. Dujardin. His explanation of the 

 Hypopus was in turn set aside by the observations of several highly com- 

 petent men, among whom were Prof. Robin, M. Fumouse and M. 

 Megnin. It will perhaps be enough to cite briefly the work of the latter. 

 He witnessed the transformation to the Hypopus of a species of Tyrogly- 

 phus, when the mushrooms, on which they were feeding, were allowed to 

 dry. Upon supplying moist mushrooms, the Hypopi transformed back 

 to Tyroglyphi. Twenty times he witnessed these transformations. It 



