MR. G. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUS2E. 
195 
Thus, for instance, if such an incision be carried across the whole diameter of the sub- 
umbrella, so as entirely to divide the excitable tissues into two parts while the 
gelatinous tissues are left intact, the result of course is that physiological continuity 
is destroyed between the one half of the animal and the other, while the form of the 
whole animal remains unchanged; the much greater thickness of the uninjured 
gelatinous tissues serving to preserve the shape of the umbrella. But although the 
contractile sheet which lines the subumbrella is thus completely severed throughout 
its whole diameter, it again re-unites, or heals up, in from four to eight hours after the 
operation. 
For a more careful study of this process of healing I adopted the following mode of 
section. With a pair of scissors I cut out the ovaries of the animal, so converting the 
latter into a broad open ring. This ring I then cut through by means of a single 
radial cut, thus converting the Aurelia into a single broad band. With a sharp scalpel 
I now carried an incision across this band, taking care only to sever the thin layer of 
excitable tissue, while leaving the gelatinous tissue uncut. The first effect of the 
operation was that of making the two edges of the excitable tissue to gape apart from 
one another, so revealing the clear underlying gelatinous tissue.Physiological con¬ 
tinuity was, of course, immediately destroyed at the line of incision. But after an 
hour or two a slight tumefaction of the gelatinous tissue caused the gaping in the 
excitable tissue to become less marked, and eventually the edges of the latter were by 
this means brought into apposition. Generally in about six hours after the operation 
some part or parts of the incision through the excitable tissue had become sufficiently 
healed up to admit of the re-establishment of physiological continuity between the 
previously discontinuous parts of the strip—contractile waves now coursing all the way 
along from end to end of the strip. At this stage it might be observed that as each 
wave of contraction passed across the line of incision, the parts of that line which had 
not yet adhered together gaped away from each other. But the healing process rapidly 
continuing, adherence rapidly extended along the whole line of incision, and generally 
in from twelve to twenty hours this adherence was complete. By observing carefully, 
however, there might still be seen a cicatrix marking out tire fine of previous incision, 
though in the course of next day this too disappeared, leaving no trace behind of the 
previous injury. 
It is an unfortunate circumstance that I found it impossible to procure any micro¬ 
scopical preparations of these lines of incision, owing to the fact that all the hardening 
and staining reagents immediately caused the newly-healed muscle-fibres again to 
rupture. After many trials I was therefore at last obliged to satisfy myself with an 
examination of the newly-healed tissues in their fresh state. I was particularly 
anxious to ascertain whether the physiological continuity which was thus re-established 
through narrow necks of tissue depended for its re-establishment upon the regeneration 
* “ Underlying,” because to perform the operation tlie umbrella requires to be placed with its concave, 
or excitable, surface uppei’most. 
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