12 BULLETIN OF THE 
pieces, and whose convex anterior edge commonly forms the front boun- 
dary of the head between the palpi. 
Behind the palpi are four pairs of short legs. Each consists of three 
movable segments, the proximal segment articulating with an immov- 
able basal plate (haunch). "The first pair of legs is directed forward at 
an angle of about forty-five degrees with the long axis of the body. The 
remaining pairs are nearly transverse, the hindmost inclined a little 
backward. The basal plates are very large, and each one almost meets 
its fellow in the middle line of the breast, so that there seems to be a 
double line running the length of the body in the median line below. 
These plates are quadrilateral, their outer margins oblique, their hinder 
and outer angles produced.* The first movable segment is triangular, 
the apex of the triangle pointing backward. The second and third seg- 
ments are successively smaller, and the latter is armed with two claws.t 
I discovered no anal nor genital aperture, nor could I detect any 
internal structure beyond the myriads of fat globules in the abdomen. 
Length, about one fifth of a millimetre, 
In some of the infested follicles bodies were found which are probably 
the eggs of the Demodex. They are oval or reniform. f 
History. Our parasite was first discovered by Henle§ in the hair- 
* The transverse ** double-line stripes" of Simon, which I regard as formed by the pos- 
terior and anterior margins of the basal plates of two consecutive appendages, are considered 
by Mégnin (and in this he agrees with Küchenmeister) to be epimera, to the ends of which 
the legs are articulated. He says: "C'est par suite d'insuffisance de connaissances en 
anatomie comparée des Acariens que MM. Cornevin et Pennetier comptent quatre articles 
aux pattes des Demodicidés : ils comptent à tort comme un premier article l'espace com- 
pris entre deux épiméres qui se suivent," But I see in preparations of Hypopus the same 
arrangement of parts, the haunches of either side almost meeting in the middle line of the 
breast so as to produce the appearance of breastbone and ribs, ‘This is well shown in 
Dujardin’s figures in Annales des Sciences Naturelles, 3d series, Vol. XII. Pl. 1l. Com- 
pare also the “ Hüftplatten " of Labidophorus Kramer, Archiv für Naturgeschichte, 1877, 
Pl XVI. The question whether the basal pieces are really the proximal segments of the 
limbs soldered to the sternum (a view long ago held by Miescher) or whether they are true 
sternal elementa, is a secondary one. 
+ "There is much difference of opinion with reference to the number of claws on each leg, 
Simon thought there were three, According to Miescher there are four on the two ante- 
rior pairs, five on the posterior. Wilson counts seven or eight. "The error is due to little 
projections from the claws, seen in optical section. 
+ According to Wedl and Mégnin Demodex is viviparous, and the bodies commonly sup- 
posed to be eggs are the earliest stages of the larve and are capable of motion. In some 
of those which I saw there seemed to be a distinct transparent shell within which the yolk 
had shrunk so as to occupy but a part of the cavity. 
$ Unless anticipated by Berger. At a meeting of the Académie des Sciences of Paris, 
May 19, 1845, Berger opened two sealed packages which had been laid before the society 
on the 2d of November, 1841, and the 14th of February, 1842, and which contained an 
