As regards the intimate structure of the ciliated embryo of _Bilharzia hæmatobia_, I have further to observe that, shortly after its extrusion from the shell, the hitherto loose, globular sarcode particles coalesce. This is apparently a preliminary step towards the subsequent differentiation process. Respecting the pedunculated blind sacs formed within the head, I think that we must regard the largest one as representing the stomach of the larva in its future cercarian stage. Under the 1/12″ objective I distinctly recognised, in the cavity of the central blind sac, numerous highly refracting granules, the diameter of which averaged not more than 1/12000″. The rudimentary stomach is often traceable whilst the larva is still within the egg. It measures about 1/500″ in length, including the peduncle, and 1/14000″ in breadth. The width of the narrow stalk does not exceed 1/9000″. The other two-stalked bodies appeared to have the character of _lemnisci_. They were occasionally well seen whilst the embryo was still within the egg. As regards the integument, it is easy to recognise two layers. In careful adjustments of the focus the inner wall of the transparent dermis presents a beaded appearance. These minute and regular markings do not undergo alteration during the contractions of the body of the larva. [Illustration: FIG. 19.--Outline representation of a ciliated embryo of _Bilharzia_, showing the arrangement of the water vessels and the vacuoles. Original.] A highly developed water-vascular system exists in these little animalcules. On many occasions I saw traces of this set of vessels, and in several instances I obtained a most satisfactory view of the entire series of branches. Anxious to receive confirmation of my discovery, I demonstrated the existence of these vessels to a skilled microscopist--the late Mr J. G. Pilcher, of H. M. Army. In the briefest terms it may be said that the water-vascular system of _Bilharzia_, in the larval condition, consists of two main stems, which pursue a tortuous passage from head to tail, and which, in the course of their windings, give off several anastomosing branches (fig. 19). As also obtains in the corresponding larvæ of _Diplodiscus subclavatus_, there is no excretory outlet visible at the tail.