20 HIRUDO. 
back, and sometimes the belly, was next the side of the glass, to which it 
still adhered. The mouth of the animal was frequently directed towards 
the enlargement, which was bounded by two slight contractions of the 
body. The motions continued half an hour, no covering meantime invest- 
ing the enlargement. But two small light brown glutinous drops having 
fallen down among the water of the vessel, a very thin pellicle seemed 
to be formed on the outside of the ovoidal part of the enlargement. This 
pellicle thickened over it, occupying the imterval between the two con- 
tractions, which comprehend the orifice of the oviduct. Yet no sensible 
pellicle covered it, that is, the orifice. Tenuity might render the pellicle 
invisible. Perhaps we may conjecture that the pellicle forms a capsule, 
surrounding the body of the leech, which is withdrawn through the red 
specks seen at its extremity after receiving its complement of ova or the 
matter containing them from the oviduct. The capsule was evidently 
formed outside of the animal. While it became more and more con- 
spicuous another leech in the vessel tore off a portion with its mouth ; 
when the original leech around which it was formed having contracted 
and withdrawn the head, the ragged capsule slipped over like a sheath, 
and fell to the bottom. 
The whole process was extremely singular, nor is it altogether very 
intelligible. Yet there seems no illusion. It rather indicated that the cap- 
sule was formed externally by some exudation of the body ; and the leech 
apparently straining itself to bring up something, the embryonic matter 
produced the ovoidal form of that portion comprehending the orifice of the 
oviduct. The body having discharged its contents might be contracted 
and withdrawn from the capsule, which, if entire, would remain aggluti- 
nated to the vessel. If the exudation is from the oviduct, it is not evi- 
dent how it can invest the body. The brownish drops fallen down shew 
the existence of fluid matter. 
Two years preceding the incident above related, I had an opportu- 
nity of observing the progressive formation of a capsule. It first re- 
sembled a film, through which about a third of the animal's body pro- 
truded downwards. After remaining almost quiescent, the head being 
withdrawn, the capsule remained much disordered, and shapeless. But 
