512 MR. A. D. MICHAEL ON THE 



The duct in J3. vulgaris does not come from the centre of the crescent, but from neai'er 

 the anterior end, and on the concave side of the crescent. 



The organ has a substantial tunica propria, within which, in the first described {i. e., 

 the distal) region of the organ, is a single layer of columnar cells, wliich are slightly 

 larger at their outer flattened than their inner rounded ends : in the largest part of the 

 organ in B. Basteri the cells measure about '06 mm. in length, have almost round 

 nuclei of about 5/i to 6/i placed near the outer ends of the cells, and clear darkly staining 

 nucleoli of under 2^t. With the exception of the niicleoli the orgaa only stains lightly. 

 In the first region the principal contents of the cells is extremely fine granular matter. 

 In the second, proximal, region of the organ the columnar cells, although still existing, 

 are less distinct and much more irregular; their inner ends are not rounded, but the 

 nuclei and nucleoli are still equally distinct ; this portion of the organ appears to be 

 lined with a distinct, somewhat loose, membrane, and the cell-contents are less granular, 

 more reticulate, and coarser. The histology of this organ is very similar to that of the 

 embedding-sacs. 



The Laminated Gland (figs. 18, 19,^/, & 17, 23, 39).— This gland (if it be a gland) may 

 be the homologue of Henkin's bursa expulsatoria in Trombidmm fuUginosum. I think, 

 however, that it may be safely said that it does not function as a bursa exjiulsatoria in 

 Bdella ; it arises from the penial canal near to the position where Henkin's organ 

 arises, although not in the identical place ; it may probably be regarded as an azygous 

 saccular out-jDushing of the penial canal which has come to possess thick walls and a 

 most special structure; it is, however, entirely devoid of the well-developed outer layer 

 of muscles which Henkin describes as surrounding his bursa. The essential difi"erence 

 in position of the organs in Henkin's Trombidium and in Bdella is that in the former 

 Henkin draws and describes his bursa and the duct from the azygous accessory gland as 

 entering the jienial canal on opposite sides of that organ, whereas in Bdella they enter on 

 the same side close together. There cannot be any reasonable doubt that the azygous 

 accessory gland of the one creature is the homologue of that in the other; but it is 

 necessary to consider whether it is the position of the bursa in Trombidium that is 

 different in position from the laminated gland of Bdella, or whether it is the duct from 

 the azygous gland that differs. The laminated gland of Bdella enters the anterior side 

 of the penial canal. Henkin says that the bursa of his species enters the " upperside," 

 treating the penial canal as being more horizontal than it is in Bdella ; it slopes some- 

 what in both, but is more perpendicular in Bdella. I have examined Henkin's species, 

 and it seems to me that the upperside would l)e the anterior if the canal were raised into 

 a perpendicular line, and that therefore the position of the bursa in Henkin's species is 

 not far from that of the laminated gland in mine, and therefore that it must be the 

 entrance of the duct from the azygous gland Avhich is different in the two creatures. 



I have called this organ the laminated gland on account of the apj)earance (fig. 39) in 

 section of being provided inside with a close series of lamellte projecting into the lumen; 

 it will, however, be seen below that this would not be an exhaustive or wholly correct 

 description of the internal structure. 



The laminated gland in Bdella Basteri is a sac of nearly even diameter throughout, 

 butAvith a convex, distal, blind end ; it is slightly curved longitudinally, but is circular in 



