ME. G-. J. EOMANES ON THE LOCOMOTOE SYSTEM OE MEDUSAE. 
705 
round the base of the polypite. In this way the nectocalyx, deprived of its margin, is 
converted into a continuous band of tissue, one of the ends of which supports the 
polypite. Now it is obvious that this mode of section must be very trying to nervous 
connexions of any kind subsisting between the bell and the polypite. Nevertheless, in 
many cases, irritating any part of the band a l has the effect of causing the polypite 
to perform the active random motions previously described. In such cases, however, it 
is observable that the further away from the polypite the stimulus is applied, the less 
active is the response of this organ. In very many instances, indeed, the polypite 
altogether fails to respond to stimuli applied at more than a certain distance from 
itself. For example, referring to fig 8, the polypite might actively respond to irritation 
Eig. 8. 
of any point in the division d , e, f, g, while to irritation of any point in the division 
f, g , A, i its responses would be weaker, and to irritation of any point in h, i,j , k they 
would be very uncertain or altogether absent. Hence in this form of section we have 
reached about the limit of tolerance of which the non-radial connexions between the 
bell and polypite are capable*. 
( e ) Another interesting fact brought out by this form of section is, that the tracts 
occupied by the four radial tubes are tracts of comparatively high irritability as regards 
the polypite ; for the certainty and vigour with which the polypite responds to a 
stimulus applied at one of the severed radial tubes f g, h i, or j k, contrast strongly 
with the uncertainty and feebleness with which it often responds to stimuli applied 
between any of these tubes. Indeed it frequently happens that a specimen which will 
not respond at all to a stimulus applied between the radial tubes f g, and h i, will 
respond certainly and well to a stimulus applied much further from the polypite, but 
in the course of the radial tube g k. 
(f) And this leads us to another point of interest. In such a form of section, when 
* This may also be well shown by the spiral form of section. Suppose fig. 2, Plate 30 to represent in a 
diagrammatic form a specimen of Tiarojpsis indicans seen in projection from above. A spiral cut ABC is 
carried round as far as the point C, so as very nearly, though not quite, to overlap the beginning of the cut A. 
The polypite P may now actively respond to stimuli applied anywhere in the area A, B, C, D (although the 
response would probably he more active the nearer the stimulation to D). But if the cut be now carried to I), 
so as just to overlap A, all response on the part of P will cease to stimuli applied anywhere over the area ABC. 
