12 BULLETIN OF THE 



pieces, and whose couvex anterior edge commonly forms the front boun- 

 dary of the liejid 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 degi'ees with the long axis of the body. The 

 remaining pairs are nearly transverse, the hindmost inclined a little 

 backward. Tiie basal plates are veiy 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. J 



JJistory. 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 bn.sal plates of two consecutive appendages, are considered 

 by Megnin (and in tliis he agrees with Kticlienmeister) to be ejjimera, to the ends of which 

 the legs are articulated. He says : " C'est par suite d'insuffisance de connaissances en 

 anatoniie com parte des Acariens que MM. Cornevin et Pennetier comptent quatre articles 

 aux pattes des Demotlicides ; ils comptent a tort comme \m premier article I'espace com- 

 pris entre deux cpimeres qui se suivent." But I see in preparations of Hi/pojms the same 

 arrangement of parts, the haunches of either side almost meeting in the middle line of the 

 breast so as to j)roduce the appearance of breastbone and ribs. This is well shown in 

 Dujanlin's figures in Annales iles Sciences Naturelles, 3d series, Vol. XIL PI. 11. Com- 

 pare also the " Hiiftplatten " of Labidophorm Kramer, Archiv fiir Naturgeschichte, 1877, 

 PI. XVL 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 

 hternal elements, 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 pairK, five on the ])osterior. Wilson counts seven or eight. The error is due to little 

 projections from the claws, seen in optical section. 



X Acconling to Wedl and Megnin Itemudcx is viviparous, and the bodies commonly sup- 

 poRe<l to be eggs are the earliest stages of the larva; and are capable of motion. In some 

 of those wliich I saw then; seemed to be a distinct transparent shell within which the yolk 

 had shrunk so 08 to o)!cupy but a part of the cavity. 



{ CrdesH anticipated by Bcrger. At a meeting of the Academie des Sciences of Paris, 

 May 19, MUCt, lierger opened two sealed packages which had l>een laid before the society 

 on the 2d of November, 1841, and the 14th of February, 1842, and which contained an 



