504 MR. A. D. MICHAEL ON THE 



other than any other known form, yet that they are very different in a large nnniher of 

 most important points ; and that in some of these points Bdella more resembles other 

 families of Acarina, wliile in the greater number it is entirely special, and the features 

 in which it differs from Ti'omhkl'mm cannot be homologized with any Acarus the anatomy 

 •whereof is known. Anyone looking at Henkin's figure will be inclined to sav that the 

 genital organs of the male TromhkUiwi are very complicated ; but they may almost be 

 called simple in comparison with those of Bdella. Pagenstecher came pretty near to 

 the correct drawing of the male organs of Tromhidmm ; but, as Henkin has already 

 pointed out, Pagenstecher mistook the sexes, and what he figures as the female organs 

 are really the male (17. pi. ii. figs. 12, 13, 11). 



The male organs of Bdella Basteri may be said to consist of: (1) the testes ; (2) the 

 embedding-sacs ; (3) the testicular bridge ; (4) the great mucous glands ; (5) the 

 glandular antechambers ; (6) the penial canal with its accessories ; (7) the azygous 

 accessory gland ; (8) the laminated gland ; (9) the air-chambers ; and (10) the great 

 external labia. The astonisliing part of this system is the great size and variety of the 

 accessory glands. 



I have, in several instances, purposely given neutral names to the parts ; the homo- 

 logies will be described later on. 



The Testes (figs. 17, 20, 35, 42, T) are two more or less pyriform masses on each side of 

 the creature, which, when in slfu, stand almost upright in the body, the larger ends being 

 upward and the smaller downward : at its smaller (lower) end each testis terminates in 

 a very short duct (Id, fig. 20) not clearly marked off from the testis ; these two unite and 

 form a short common duct which enters the end of the testicular bridge. The testes are 

 in the hind portion of the body, a little behind the genital opening, and are placed 

 immediately below the hind cfeca of the ventriculus. When the testes are ripe, they 

 sometimes force their Avay between the lobes of the coecum or push it aside, and thus 

 may be found pressed almost against the dorsal surface. 



The histology and construction of each of these testes bear considerable resemblance 

 to those of the whole testicular mass, on each side of the body, in Thijas petrophilus ; and 

 it must be remembered that that organ is divided into two lobes, seeming to give some 

 indication of a double origin (14. pp. 193, 194, pi. viii. fig. 17, pi. ix. fig. 28). In 

 Bdella Basteri the exterior timic of each testis, particularly where it rests against the 

 embedding-sac, and the adjoining part of its outer side {i. e., that part of the testis 

 which is most remote from its fellow on the same side of the body), is composed of largish 

 cells (fig. 35, tp), but indistinctly demarcated, containing somewhat solid plasma which 

 stains freely, and having very clear almost circular nuclei of about "01 mm. diameter, and 

 nucleoli of about 3 ^ to 4 fi. These cells usually extend over portions of the inner and other 

 surfaces ; but on the portion of the inner surface furthest from the embedding-sac, and the 

 surface opposite the sac, and the adjoining parts of the outer surface, their character is 

 entirely changed in the ripe male ; there these cells have become much more clearly 

 marked off from each other, considerably larger, and very irregular in form, the nucleus 

 has entirely disappeared, and t he cell-contents have become divided into numerous 



