Sarcostyles of the Plumularidse. 123 



are very active after certain parts of the colony have been 

 mutilated or where the hydranths are undergoing disintegra- 

 tion. While studying Plumularia pinnata at Plymouth I 

 saw astonishing exhibitions of activity on the part of the 

 sarcostyles in the vicinity of mutilated gonangia. Their ex- 

 tensibility was incredible and apparently without limit. They 

 would climb over the top of the gonangia and scour the inside, 

 they would wind round and round the stem and branches in 

 a perfect maze of apparently protoplasmic threads, and yet be 

 able to unsnarl themselves with the greatest ease, and after- 

 ward disappear entirely. Dead hydranths seemed particu- 

 larly attractive to them, and it appeared as if they actually 

 devoured or in some way absorbed the organic matter of the 

 disintegrating polyps, so that not a trace remained within 

 the hydrothecse in a very short time after the sarcostyle3 

 attacked them. 



4th. Holding together adjacent corbula-leaves until their 

 edges unite. — This is a novel use of the sarcostyle, discovered 

 by myself while working out the embryology of the corbula, 

 or fruit-receptacle, of Aglaophenia pluma at Plymouth. The 

 corbula is a pod-shaped structure, made up of a number of 

 ribs or leaves, which are separated first, but afterwards 

 coalesce to form the mature corbula. Along the edges of 

 these leaves are rows of nematophores. 



While examining a young corbula of a living colony, I 

 noticed that the sarcostyles along the edges of the leaves were 

 exceedingly active, and that they were stretching across from 

 one leaf to the next, to which they adhered by their adhesive 

 ends. " It appeared as if these sarcostyles served as a 

 temporary attachment to hold the edges of the two leaves 

 together, while the edges themselves were connected by 

 trabeculae of coenosarc which rapidly formed a stronger and 

 permanent connexion. The perisarc of the edges of the 

 leaves seemed exceedingly thin and in places appeared to be 

 wanting. A contact having been established between the 

 adjacent leaves, the permanent attachment was soon formed 

 and the ccelomic cavities of the leaves established connexions 

 at these points. A little later currents of water bearing 

 granules were seen to flow in active streams from one leaf to 

 the other " *. 



In this case it appeared as if the sarcostyles served to hold 

 the edges of the leaves together while the permanent con- 

 nexion was being established, after which the sarcostyles 

 loosened their hold and retracted into their respective nemato- 

 phores. 



* C. ('. Nutting, " Notes on Plymouth Hydroids," Journ. Marine Biol. 

 Assoc, February 1896, p. 153. 



