ON THE DEVELOPMENT OF BILHARZIA HiEMATOBIA. 643 
Taenia cyathiformis infesting the swallow, in Tania variabilis 
of the gambet, in Octobothrium lanceolatum attached to the 
gills of the common herring, and in Polystoma appendiculata 
from the branchiae of various marine fishes. Characteristic 
examples of the eggs of parasites which, like Bilharzia , are 
furnished with a singular appendage, may likewise be seen 
in the ova of different species of Bactylogyrus infesting the 
gills of the pike, and also in the eggs of Biplozoon paradoxum, 
where, moreover, the variations of the degree of development 
of the holdfast are much more striking than anything we 
have seen in the eggs of Bilharzia hamatobia. In the more 
strongly pronounced developments it is easy to perceive how 
admirably adapted are these outgrowths of the egg for the 
various necessities of the different species of parasite to which 
they are severally referable; and, even in the case of Bil¬ 
harzia , the trifling amount of anchorage furnished by a pro¬ 
jecting point is not absolutely thrown away. The resistance 
will also be greater where the spine is situated a little on one 
side of the pole of the egg, which in many instances seems 
to need steadying during the violent struggles of the embryo 
to escape from its temporary abode. 
When any considerable number of ova are removed from 
the urine and examined together, it will be found that 
a large proportion of them contain embryos in a more or less 
advanced stage of larval growth. The structural appearances 
presented by the embryos whilst still in the egg are remark¬ 
ably uniform ; since, in all, the yelk appears to have resolved 
itself into a mass of rounded or oval sarcode-globules, one or 
two of these particles being conspicuously larger than the rest 
(Figs, h, Jc , 0 ). At this stage, except at the cephalic division 
of the lava, no tendency to differentiation of the sarcodic 
contents is perceptible; but, some time after the embryo has 
escaped, one may notice elongated masses of sarcode formed 
by the coalescence of the globules. Whilst still in the egg, 
one end of the primitive embryonal mass becomes gradually 
narrowed, cilia at the same time making their appearance. 
This part becomes the future head, which eventually acquires 
a distinctly conical figure. Whatever form the body of the 
embryo may display after extrusion from the shell, the head 
retains its conical shape; the cone itself being narrowed or 
widened, as the case may be, only when the larva is sub¬ 
jected to abnormal conditions (Fig. m, n , q). Whilst the 
head is undergoing its development within the shell, one, 
two, or sometimes three, pyriform masses make their appear¬ 
ance within the cone; and after the embryo has escaped the 
shell, these structures become more marked, being at all 
