345 
the Hiriido complanata and Hirudo stagnalis. 
themselves, they do not prove productive ; hence there seems 
to be a necessity for this parental solicitude. This pouch, or 
cavity, is always conspicuous in the G. punctata, but in the G. 
tuherculata, only at the time of its producing young. When 
the young are excluded from the ova, they remain attached 
to this cavity by the tail, enjoying a free extent of motion 
with the rest of the body. In this position they are repre- 
sented in Fig, 7. They frequently leave this pouch, but 
soon return, and again affix themselves. Shortly after birth, 
their interanea are filled with a cream coloured fluid, which, 
under the microscope, presents a most interesting and beau- 
tiful appearance. Whilst speaking of the stomach of the 
parent animal, I forgot to observe, that the interanea are only 
visible when food has been recently taken. I mention this 
circumstance, that I may not be supposed to labour under a 
mistake, in the view I have given of this organ. Muller 
himself indeed confesses, that he was a whole month (al- 
though assisted by the microscope) before he discovered it, 
yet he with much candour adds, that he afterwards very fre- 
quently saw it, even with the naked eye. 
JAMES RAWLINS JOHNSON. 
London, June 18, 1817. 
Explanation of Plate XVII. 
Fig. 1 , q. The G. tuherculata , natural size, front view. 
Fig. 3, 4. Ditto, back view. 
Fig. 3. The tubular tongue ( magnified ) : that portion 
from a to b is usually protruded from the mouth, the letter 
Y y 2 
