270 REPORT ON THE PENNATULIDA. 



growing? up like a young tree, and on offering to pluck it up it shrinks 

 down to the ground, and sinks unless held very hard. On being plucked 

 up a great worm is found to be its root, and as the tree groweth in 

 greatness so doth the worm diminish ; and as soon as the worm is 

 entirely turned into a tree it rooteth in the earth, and so becomes 

 great. This transformation is ono of the strangest wonders that I saw 

 in all my travels ; for if this tree is plucked up while young, and the 

 leaves and bark stripped off, it becomes a hard stone when dry, much 

 like white coral : thus is this worm twice transformed into different 

 natures. Of these we gathered and brought home many." 



These accounts are of great importance, as they prove beyond 

 all possibility of doubt that the erect position is the normal one for 

 Virgularia, and if so, it follows with almost absolute certainty that 

 the same must be the case with other allied and similarly constituted 

 genera. 



2. — On the Potcer of Retraction. — This, also, is a point of very consider- 

 able interest and importance. It will be noticed that both Darwin 

 himself and Captain Lancaster, in the accounts quoted above, state that 

 Virgularia has the power of retracting suddenly into the sand when 

 disturbed " so as nearly or quite to disappear." Rumph says exactly 

 the same of V. juncea, which he describes as burying itself at low 

 water so far in the sand that only a bit of three or four fingers' 

 breadth projects. 



We do not yet know whether V. inirabilit; also possesses this power 

 of retracting partially or completely into the mud when disturbed, but 

 from analogy it would appear by no means improbable that it does so. 

 The possession of this retractile power is clearly very advantageous for 

 the sake of protection, and it will be an interesting point for future 

 observation to determine whether this power is in any way a compen- 

 sation for the loss of the more usual means of defence — i.e., thread-cells. 

 We have but little evidence on this point as yet. Kumph distinctly 

 states that V. juncea does not sting, but does retract forcibly when 

 disturbed : while V. Rumphii, which possess very marked stinging 

 powers, is not mentioned as retracting. 



Supposing, which seems probable, that T'. mirabilis possesses this 

 power of retracting partially into the mud, it would help to explain 

 why the lower halves of the rachis escape, although the tops are so 

 constantly eaten off. 



Concerning the mechanism of retraction it is difficult to form any 

 precise idea. From the descriptions it would appear to be a muscular 

 action effected probably by the powerful muscular system of the stalk 

 and rachis. 



Some experiments made by Dalyell show well the efficiency of these 

 muscles. He found that in living specimens the muscles of the 

 rachis frequently cause the fleshy part to twist itself in a spiral 

 manner round the stem, and then straighten out again. " A section, 

 six or eight inches long, standing inclined in a narrow jar, will be 



