SECTION OF COVERED-EYED MEDUSZ. 83 
short duration, the blocking will most likely be 
transitory. Even the slight strains caused by hand- 
ling a contractile strip in the air are generally 
followed by a decrease in the rate of the waves, and 
sometimes by their being completely blocked. Other 
methods by which the passage of waves in contrac- 
tile strips admits of being blocked will be alluded 
to farther on. 
Now, in all these cases of temporary blocking we 
must conclude that when the contraction-waves 
succeed in at last forcing a passage, some structural 
change has taken place in the tissue at the region 
of injury, corresponding with the functional change 
of the re-establishment of physiological continuity. 
The waves previously stopped at a certain point of 
section or otherwise, after beating for a time on the 
physiological barrier, are at last able to throw down 
the barrier, and theneeforward to proceed on their 
way unhindered. What, then, is the nature of the 
structural change which has taken place ? 
In the early days of this research, before the 
presence of a nerve-plexus had been proved histo- 
logically, I argued in favour of such a plexus on the 
grounds furnished by many of the foregoing ex- 
periments; and at a lecture given in the Royal 
Institution I ventured to say that if a careful 
investigation of the histology of these tissues should 
fail to show the plexus which the result of those 
experiments required me to assume, we should still 
be compelled to suppose that the plexus was pre- 
sent, although not sufficiently differentiated to 
admit of being seen. I further ventured to suggest 
