INTERNAL ANATOMY OF BDELLA. 493 



The general nature of tlie glands and their arrangement will be found, as might be 

 anticipated, to correspond to a great extent with those of the Trombidiidaj and 

 Hydrachnidie, but the diflerences are considerable. 



In Bdella this system of glands may be said to be divided into three groups ; of these 

 there are two grouj^s of paired glands and one single azygous gland. The general 

 arrangement of these glands and ducts will probably be best understood from the drawing 

 (fig. 8) ; it must, however, be stated that this is a diagram in the sense that (to save 

 space) it is not drawn quite to scale, although kept as near nature as possible. Group 1 

 consists, on each side of the body, of three glands, which viltimately discharge by one 

 common duct (D), each gland and duct being paired by its fellow on the opposite side of 

 the body. The exact shapes of the respective glands vary a good deal in different 

 individuals, and probably in the same individual at different periods. One of these 

 glands is placed at the posterior end of the main common duct, and is in position a con- 

 tinuation of the duct ; this gland is what is known as the " tnhnlar salioary glantV {sfft) i n 

 Tromhidium, the Hydrachuidae, and other forms. It is far simpler than the corresjjonding 

 structiu-e in Thyas j^etrophilus, and in B. Basterl consists of a tubular or sausage-shaped 

 gland having a diameter of from about "03 mm. to al)out '00 mm. and a less varying 

 lumen of about 015 to "02 mm. It has thick fleshy walls composed of moderate-sized 

 cells with small clear nuclei. The lumen of this gland is extremely small, but perfectly 

 distinct. The point where the duct emerges from the gland is between tiie first and 

 second legs, usually about halfway or rather nearer the first leg ; thence the gland runs 

 almost straight backward near the side of the body ; this course is continued for more 

 than half tlie length of the gland, then it curves sharply inward, and the curve is 

 continued so as to Ibrm an approach to a semi-circle ; thence the gland runs forward 

 again parallel to its former course, but nearer to the median line of the body ; it does not, 

 hoAvever, reach anything like as far forward as the proximal end from which the duct 

 starts. Einally, the gland once more turns backward and again runs parallel to its 

 lormer coiuse, so that the whole gland is more or less S-shaped. The distal end is 

 csecal and rounded ; from it and also from the first bend fine ligaments run to the side 

 of the body ; that from the first bend, whicli is the strongest, runs to the cuticle near 

 to the inner edge of the acetabulum of the first leg ; this to some extent resembles the 

 arrangement described by Schaub in llijdrodroma (i8. his p. 123 and fig. 4) ; the ligaments 

 at and near the distal end of the gland run to the cuticle further back in the body. 



In Bdella Basteri this gland bears a short caecum {ca's). The whole gland in Bdella 

 is quite simple, without any of the corrugations found in 1 ht/as jjetmphilus din^i othev 

 forms, and without the terminal bladder or reservoir found in that species. 



The Main Common Duct (D) starts from the anterior end of the tubular salivary gland 

 {s(jt), and runs attached to, and during a large part of its course partly imbedded in, the 

 cuticle of the side of the body. Although so vmited to the cuticle and so sunk in it, the 

 duct does not really form part of it ; on the contrary, the greater part of the duct may 

 occasionally, by careful dissection, be detached from the skin. The duct is substantial 

 in the thickness of its waU, and usually preserves its round form in sections — i. e., it does 

 not collapse : it generally shows more or less of a ringed structure ; often it is very 



SECOND SEllIES.— ZOOLOGY, VOL. VI. 67 



