274 Mr. E. A. Minchln on the 



tlie fact that wlien the organs are placed in spirit tlicy become 

 at first exceedingly sticky, and adhere to one another and to 

 everything they touch ; so that in spirit-specimens perfectly 

 misleading appearances are obtained. 



If a Ilolof/nirm nigra be opened fresh in sea-water, it is 

 easily seen that the Cuvierian cteca are each quite separate 

 from one another and arise independently from the left respi- 

 ratory tree (PI. XVII. fig. 9, c.o. and I.rsp.). In the normal 

 condition they are cylindrical, tapering to a point at tlieir 

 distal extremity. For the most part tliey are of a pure white 

 colour, but a few are pinkish in tint. The latter are probably 

 freshly formed as outgrowths from the respiratory tree. A 

 healthy animal always contains an enormous number of tubes, 

 and they take up a very large space in the body. 



2. Phenomena of Elongation. — The most curious property 

 of these 'organs is their power of elongating to a relatively 

 enormous extent. I will first describe what is seen in the 

 living animal. 



If a healthy Holotliuria nigra be pricked with a needle it 

 first draws in Its tentacles and ceases to move. If the stimu- 

 lation be continued it slowly curls the posterior part of the 

 body up towards the part affected. In a few moments a 

 number of white threads are seen to emerge from the anus 

 and to rim about swiftly In all directions. At the end of 

 each thread is a thicker portion or head (A, figs. 1 a and h)^ 

 which is easily seen to be the cause of the movement; for 

 the thread itself is formed continuously from it at the point 

 .T, and the head gets smaller and smaller during the process. 

 When first ejected the head averages about 2 centimetres in 

 length. Since the head produces perhaps twenty times Its 

 own length of thread or more, it rushes through the water by 

 its own activity. One might compare the head to a rocket 

 and the thread to the trail of sparks emitted by it. More- 

 over, as the head is generally slightly curved, it runs in any 

 direction. The result Is that the irritating body gets enve- 

 loped in a network of delicate but exceedingly tenacious and 

 sticky threads. As Is well known to the Plymouth fishermen, 

 even animals as large as lobsters become so firmly entangled 

 that they are unable to move. Meanwhile the Holothurian, 

 if the Irritation has ceased, walks quietly away, and the 

 Cuvierian threads, as we may call them, being now firmly 

 fixed to some foreign body, break off at their attachment to 

 the respiratory tree. As a rule only a small portion of the 

 tubes contained in the body are emitted at a time, and a 

 healthy Holothurian can emit them live or six times In succes- 



