482 ME. A. D. MICHAEL ON THE 



internal anatomy of other memhers of that group must also he kept in view ; they will 

 he found constantly referred to helow, and it will he seen that although Bdella differs 

 widely from these types, it resemhles them more than it resemhles any other Acari. 

 The principal works on the internal anatomy of these allied creatures ai-e those hy 

 Croneherg (4, 5), Henkin (6), Pagenstecher (17), Schauh (18), and myself (14)- 



The Trophi and Mouth-okgans. 

 (Eigs. 1, 2, 4., 29, 30, 31, 32.) 



Maxillary Lip and Exoskeleton of Bostrimi. — The extremely elongated rostrum 

 of Bdella consists of a long, chitinous maxillary lip (fig. 29), very conca^-e iijjward, 

 i. e., it is a half-tuhe with its convex side downward ; toward its proximal end it swells 

 out greatly, hoth laterally and helow^ so as to form a hull) — or perhaps it would he more 

 correct to say a half-hulh, the similar and superposed swelling-out of the mandibles 

 forming the other half-hulh. The edges of this lij), except near the anterior end, curl over 

 inward ; the portion so turning inward is flat, forming a partial roof to the rostrum ; 

 above the bnlhoiis p)ortion of the lip these two flat pieces, one from each side, fuse, forming 

 a perfect roof to that part of the rostrum (fig. 4) ; at its posterior edge this roof is 

 strengthened hy a curved bar of thicker chitin, which in Trombkliiim Heukiu calls the 

 " Chitiuhriicke " ; and about one-fourth of the distance from the bar towards the anterior 

 end there is a longish spinelying flat upon and articulated near the edge of the roof. 



The anterior end of the maxillary lip is truncated abruptly ; its edge being almost a 

 semi-circle convex downward, or even with the sides pressed together a little ; but the 

 half-moon-shaped space thus left does not remain open to the exterior. Kramer and 

 Karpelles following him draw the anterior edge of the lip as armed with a sei'ies of 

 spines, w'hich are a continuation of the edge of the lip itself (see Ki-amer's fig. 5, c ; 

 Karpelles' fig. 2), and Kramer suggests from this supposed formation that the lip is a 

 piercing-organ. I do not find the arrangement so simple as this in those species which 

 I. have examined : taking B. Basterl as an example, I find that inside the edge on each 

 side, partly within the chitinous lip and partly protruding beyond it, is a very fine and 

 extremely transj)arent membranous flap (fig. 32, iiif) ; on the inner side of this flap is a 

 series of strong hairs or fine spines, all curved inward, especially near their tips. 

 Fig. 32 shows the maxillary lip flatteaed out so as to exhibit these flaps ; but when it is 

 in its natiu-al shape the curvature causes the flaps to stand nearly on edge, and they 

 slope slightly inward so as to touch at their anterior edges, and the curved ends of the 

 hairs cross, thus closing the mouth-opening and excluding dust, &c. (fig. 29), w^hen the 

 lingua is not protruded ; when it is, it forces these flexible flaps apart. This apjiaratus 

 is much more correctly drawn by Berlese (i), see his figs. 3, 4 It, and ^ g ; he calls it 

 sometimes "galea," sometimes "lacinia"; it also has considerable resemblance to 

 Henkin's " reusenformiger Apparat der Mundoffnung " in Trombidimn. 



From near the edge of the chitinous maxillary lip, on its outer (under) side, spring two 

 chitinous apophyses on each side of the lip ; I'rom each apophysis a strong, curved, tactile 

 hair (tigs. 29, 32, thl) springs, which projects beyond the edge of the membranous flap. 



