508 ME. A. D. MICHAEL ON THE 



marked, usually nearly circular nucleus, wliicli averages about 10 ^ and has a large 

 distinct nucleolus of about 5 ^ to 6 /.i. The remainder of the cell is either entirely or partly 

 filled with a finely granular secretion, whicli shows the largest granules near the exterior 

 of the cell, bvit in the lumen of the organ becomes very homogeneous, and which stains 

 but slightly ; or else is completely empty; the latter is the commonest condition. I say 

 very homogeneous in the lumen, but of coxxrse a sufficient power shows this secretion to 

 be granular even there, but as the granules are not above i n in diameter and extremely 

 hyaline, it requires a comparatively high power of the microscope and some definition to 

 see them clearly. What apparently takes place is that when the secretion is formed the wall 

 of the inner end of the cell breaks down and the contents are discharged into the lumen of 

 the organ, which is often quite full of it, although at other times empty. After the wall 

 of the inner end of the cell has broken down and discharged its contents the other walls 

 persist, forming deep pockets, so that the whole strvxcture looks like an almost empty 

 honeycomb ; into these pockets the secretion continues to be discharged and to find its 

 way thence into the lumen. 



These organs do not vary much in the other species of Bdella which I have been able 

 to examine ; the principle and histology have always been the same; the chief difference 

 which I have found has been that in some species, particularly the smaller ones, the 

 organ is often thicker (i. e., has a larger diameter) in proportion to its length, and that 

 the two parallel portions are consequently shorter and are more pressed against each 

 other ; the result of this is that the whole mass, even in section, looks more globular. In 

 some sj)ecies, e. g. B. vulgaris, it would be possible for a person seeing only the section 

 to overlook the fact of its being a sausage-shaped organ folded on itself, and to take it 

 for a globular one, if he had not seen B. Basteri or some other similar species to guide 

 him to the true form ; of course a careful examination would reveal the true conformation 

 of the organ in any species. 



There are two passages, and two only, ovit of, or into, each mucous gland ; these are at 

 the two ends. In the upper more rounded end, but not median in that end, there is a 

 very small but perfectly distinct entrance to the glandular antechamber (vestibulum 

 glandulae mucosai) (fig. 19, v(j), Avhich entrance is ordinarily kept closed by the thick 

 walls of the antechamber itself being pressed against one another. About the centre 

 of the lower more lobose end is a much smaller passage ordinarily very tightly closed 

 by a sphincter, which leads into the testicular bridge. Hound this passage a few cells of 

 the mucous gland have usually entirely broken down, their latei'al walls even being 

 destroyed ; thus an open space is left, \\ hich is generally wholly or partially filled Avith 

 the secretion, unless the lumen of the organ be empty. 



The Glandular Antechambers {vestibulum (jlandiilm mucosa;) (figs. 20, 36, 38, vg, & 17, 

 18, & 41) are two paired chambers, one leading from the upper end of each of the great 

 mucous glands into the head of the penial canal : each antechamber is almost in a line with 

 the part of the mucous gland Irom which it springs, but turns slightly upward to reach the 

 dorsal side of the head of the penial canal and to escape the edge of the testis; it is sharply 

 divided from the uiucous gland by the constriction which forms the narrow passage before 

 mentioned, and from the penial canal by a similar constriction ; so that it becomes an 



