50 PARASITES OF MAN 



spine into the tissues of a mollusk, and shall have become 

 metamorphosed into a sac-like larva (Nurse, Sporocyst, or Redia, 

 as the case may be). Whatever be the full significance of these 

 internal developments, we have at least satisfactory evidence 

 that the complete and free embryo is a globe- 

 shaped animalcule, having the anterior third 

 or cephalic end of the body covered with cilia, 

 and armed with a central boring spine. In 

 consequence of this limitation of the ciliated 

 covering, its swimming movements are less 

 FIG. is -ciliated em- vivacious than those of the embryo of Fasciola 

 c2iatl^b a iluc: hepatica ; it will, therefore, probably take up 

 its residence in a less active host than that 

 chosen by the embryo of Fasciola, selecting one of those mollusks 

 which either move slowly or are prone to keep at the bottom 

 of the water. The mature eggs have a length of ^ 5 to ^ of an 

 inch, and a breadth of 5 jj". The long diameter of the free 

 embryo varies from ^ 5 " to g y, the transverse diameter being 

 7353". Whilst the embryos were still in the egg Leuckart could 

 see no ciliary motion. With most observers, both the ciliary 

 apparatus and the boring spine appear at this stage to have 

 altogether escaped observation. 



A's regards the intimate structure of the ciliated embryo of 

 Bilharzia hamatobia, 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. Respect- 

 ing the pedunculated blind sacs formed within the head, 1 

 think that we must regard the largest one as representing the 

 stomach of the larva in its future cercarian stage. Under 

 the ' objective I distinctly recognised, in the cavity of the 

 central blind sac, numerous highly refracting granules, the 

 diameter of which averaged not more than y^/'. The rudi- 

 mentary stomach is often traceable whilst the larva is still within 

 the egg. It measures about 5 J 5 " in length, including the 

 peduncle, and ,4 55 " in breadth. The width of the narrow stalk 

 does not exceed ~ 05 ". 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 



