524 Georgiva Stveet : 



tissue around the roots of the pectoral blood-vessels and m the 

 pericardium by Dr. T. S. Hall, who brought them to me. 

 Careful examination of them and consultation of such literature 

 as was available to me, showed that these forms are really the 

 " hypopial nympha," or second stage in the life-history of one 

 of ihe feather-feeding Sarcoptidae, proljably of Falculife.r 

 rostratus (Buchholz, 1869), Railliet, 1896. 



This and similar forms — known variously as Acavan luus- 

 carus, Linn., Acarus sjiinitarsus, Hermann, 1757, then Hypo- 

 pus, Duges, 1834: ; Homopus, Koch, 1843, and later as Hypo- 

 dectes, Filippi, 1861, and Hypoderas, Frauenfeld, 1864 — have 

 been the subjects of a long discussion, dating from 1735, but 

 closed for the time being by the Avork of Megnin (1879, p. 120) 

 and that of Michael (1884, p. 371). 



Tliese parasites, as previously described by several — viz., 

 Michael, and also figured by Ch. Robertson (1866, p. 201) — are 

 white, elongated, rounded animals, anaggot-like in general 

 appearance, .92 to 1.24 mm. long, and .16 to .31 mm. wide. 

 The skin is soft and easily wrinkles. No median transverse 

 groove was visible, nor were rostrum, mouth appendages or ali- 

 mentary canal to be seen. Four pairs of short jointed legs are 

 present, the two posterior pairs being situated a considerable 

 distance behind the 2 anterior jDairs. Each leg has 5 joints, 

 not always clearly defined, the last bearing a number of hairs, 

 one or more of these hairs being much longer than the others. 

 The bases of the two anterior pairs of legs are associated with 

 a curious darkly coloured chitinous-like support on the ventral 

 surface of the head, while another similarly constittited but 

 differently arranged structure is found on the ventral surface of 

 the body, betv/een the 2 posterior pairs of legs. These two 

 masses form a most conspicuous and characteristic feature in 

 the appearance of the parasite. The form here recorded is 

 closely similar to that figured by Robertson, l)ut I am adding 

 hereto two figures, one of the dorsal surface of the head, and 

 one of the ventral surface of the body, for comparison. As J 

 have not the adult stage of this form, I luive iiot been able to 

 completely verify tliis identification. 



According to .Mcgnin's researches (loc. cit., and see also 

 Neumann, p. 214), tliis much reduced form is a iictuliar stage 



