47 
P. Manson-Bahr and N. H. Fairley 
of progression, but as an organ with an alimentary function. Where the worms 
do not entirely block the vessel, it is possible that their tuberculated skin 
enables them to maintain a stationary position against the blood stream. 
When desirous of depositing ova, the female protrudes herself from inside 
the gynaecophoric canal, and migrates in the manner described above, until 
she reaches a very fine branch. It is obvious that her smaller diameter enables 
her to do this with comparative ease, and when the diameter of the vein limits 
her progress she ejects her ova through her genital aperture, as shown in the 
diagram (Text-fig. 3, a and b). In the case of the S. mansoni these are few 
in number, but in the case of S. haematobium they are much more numerous. 
The greatest number of lateral spined ova noted in a venule has been six, 
whereas fully twenty terminal spined ova may occur actually jammed into 
one vessel. In each case the spine is directed towards the larger diameter of 
the vessel, i.e. in the direction of the flow of the portal blood. 
Now the transverse diameter of the anterior truncated part of the female 
Text-fig. 3. Diagram representing method of deposition of ova into the lumen of a small Vein by 
the female and their subsequent passage through the vessel wall: A in the case of S. mansoni, 
and B in the case of S. haematobium. 
1. Anterior sucker. 2. Posterior sucker. 
3. Vaginal orifice. 4. Uterus with contained ova. 
woim v hen stietched out m this manner becomes not very much greater 
than that of the deposited ovum, therefore it follows that these eggs must 
be in very close apposition to the walls of the vessels. By blocking the vessel 
in this manner the blood current in the vein, which has become stretched to 
accommodate the worm, becomes arrested. 
When the female worm withdraws from the smaller branch vessel into 
which she has worked her way, towards one of larger diameter where she 
has left her male partner, the vessel wall immediately contracts down to its 
normal size and thus comes into contact with the deposited ovum : in conse¬ 
quence, there is every probability that the spine of the ovum will engage the 
vessel walls. Reflex spasm of the muscular tissue of the wall is an additional 
factor for ensuring this result. Apparently, after withdrawing a little, the 
female again becomes stationary; this act is again repeated, and in -this 
manner a whole senes of ova are deposited in small vessels °'ivin°' the 
appearance of a string of sausages in miniature. The final withdrawal of the 
