THE CUVIERIAN ORGANS OF HOLOTHURIA NIGRA. 303 
largely on whether the undischarged organ is filled with 
water or not. 
By introducing a fine glass cannula or a hypodermic needle 
into the base of an undischarged organ and injecting fluid, 
the tube is shot out in precisely the same way as in a normal 
discharge by the living animal. The elongation can be 
stopped at any stage by reducing the water-pressure and 
continued by increasing it. When a coloured liquid is used 
for injection it is often seen to pass up to the tip of the organ 
before elongation starts, showing that the lumen is patent 
throughout the undischarged tube. Examination with a low 
power of the microscope shows transverse thickenings in the 
wall of the undischarged tube, suggesting that it is folded 
together rather like an accordion. 
The inset in Fig. 5 shows an undischarged organ with a 
hypodermic needle inserted into its lumen. The rest of the 
figure shows the effect of injecting it partially with sea-water. 
Fig. 6 gives another example more completely injected, in 
this case with air. 
A comparison of the appearance of the tubes discharged 
normally by the living animal with those artificially injected 
with sea-water reveals no point of difference, but more striking 
still is the exact similarity of the movements under the natural 
and experimental conditions. 
The pressure needed to cause elongation of the tubes is 
about 20 or 30 cm. of water. A pressure of 15 cm. sufficed 
to cause partial elongation of a tube, but failed to shoot it out 
completely. 
It is easy to observe that during the discharge of tubes by 
the living animal, the body of the latter is always tense and 
firmly contracted. 
In several experiments I have demonstrated the rise of 
internal pressure in Holothuria on irritation by the following 
device: A thin rubber balloon attached to the short limb of 
a long glass tube bent at right angles was introduced in a 
collapsed state through the oral aperture, and thrust into the 
body-cavity with the aid of a blunt instrument. The balloon 
