June-Sept. 1S94.." 



PS 7 CHE. 



97 



Later Megnin alone ('79) published 

 an extL'nsive memoir on the mites of 

 the cellular tissue of birds. Therein he 

 reviews the work of many of his prede- 

 cessors and adds to his own previous 

 contribvitions a more extended account 

 of this stage and of its relation to tlie 

 life histor3'. Megnin had found in 

 Lop/iyrus coro>tatus Vieill. not a 

 single form but two, one of which he 

 showed to be the male nvmph of Ptero- 

 lichus falciger; the other he was 

 inclined to regard as the female nymph 

 of the same species on account of its 

 strong resemblance to the normal 

 female. Mt'gnin explains the occur- 

 rence of these forms in the cellular 

 tissue in the following way: 



So long as the conditions of existence 

 remain the same, the succession of 

 stages in the life history of the mites is 

 invariably egg, larva, normal nymph, 

 male or female, and then the egg again. 

 If, however, the conditions change, if 

 the food or shelter necessary to life 

 begin to disappear, the colony seems 

 doomed to destruction. Certain species 

 escape that fate, thanks to a curious 

 biological phenomenon which we dis- 

 covered and named adventitious or 

 hypopial metamorphosis. This has 

 been found to occur In four species of 

 Tyroglyplius and in one of Ptcroli- 

 chtis, P. falciger, a plumicolous sar- 

 coptide of the pigeor^ . . . Wlien 

 a pigeon invaded by a colony of these 

 mites begins to pull out its feathers, the 

 mites are deprived of shelter and of the 

 secretions which serve them as food, 

 the normal life cycle is arrested and the 



normal nymph instead of giving rise to 

 a male or female increases in size and 

 brings out of its skin a new form, fitted 

 to a new mode of life. This form is 

 worm-like and has been described and 

 figured under the name of an adventious 

 or hvpojjial nymph ; it introduces itself 

 into the follicles of the feathers, or even 

 by the respiratory organs and reaches 

 the cellular tissue, especiallv the peri- 

 tracheal, which is very loose in birds. 

 Here it lives and grows by absorption, 

 for it has neither orifices nor internal 

 organs, and returns to the surface only 

 when the normal conditions are estab- 

 lished. 



Megnin found a normal nymph of 

 PtcrolicJius falciger enormously de- 

 veloped and in process of metamorpiio- 

 sis ; it contained the larger hypopial 

 nvmph. As to the nature of the 

 smaller form which is supposed to be 

 the hypopial nymph of the female, he 

 was not able to furnish axw direct 

 proof. 



Trouessart et Megnin ('S5) in their 

 revision of the group, ha\'e placed the 

 adult, of which Hypodectes is the 

 hypopial nymph, in a new genus, Fal- 

 ciger. 



Murray ('77) refers to the form found 

 in the pigeon under the generic name of 

 Hypoderas ; but his description and 

 figures are entirely inadequate for iden- 

 tification. 



In the United States this form has 

 been reported seveial times. H. Gar- 

 man ('84) was the first to record its 

 occurrence. He described it under its 

 proper name, and recognized its nym- 



