CONTRIBUTION TO KNOWLEDGE OF RHABDOPLEURA. 637 



polypides, which succeed one another in the same way as we 

 pass further and further backwards along the stalk (see PL 

 XXXIX, fig. S) where the buds are numbered^ and fig. 1). If 

 we had a complete colony under study we should, in thus fol- 

 lowing back the stalk, come to its original starting-point, the 

 point at which the embryo Rhabdopleura fixed itself when it 

 began to assume the form of a polypide. Of this commence- 

 ment I am not able to give any account; the oldest parts of 

 the colony appear to have died down and broken away in all 

 my specimens. Remarkably enough, the allied genus Cepha- 

 lodiscus of Mcintosh helps us to picture to ourselves the 

 earliest condition of the Rhabdopleura colony, for in Cephalo- 

 discus no colony is ever formed, but the polypide-stalk (about 

 as long as its body) produces two buds near its base, which 

 after attaining the form and a third the size of their parent, 

 become detached. If the buds of Cephalodiscus were to remain 

 attached to their parent, and did the parent's stalk elongate 

 and continually produce new buds from its newly-grown region 

 (that furthest from the original termination of the stalk) whilst 

 the older region became cuticularised, we should have some- 

 thing like a Rhabdopleura colony without a tubarium. Cepha- 

 lodiscus does not form a tubarium, but numerous detached 

 individuals are sunk in cavities in a thick gelatinous substance, 

 which forms a common investment to a vast number of separated 

 free polypides, and has the same value morphologically as the 

 tubarium of the Rhabdopleura.^ 



To return to the proliferous branch of Rhadopleura. As 

 soon as one of the very young wart-like buds has attained a 

 certain size, a transverse septum of very delicate chitinous 

 lamellae is thrown down across the tubarium immediately behind 

 it (/ in fig. 1, and just behind 3 in fig. 3, PI. XXXIX). I am 

 inclined to think that the septum is secreted by the epiderm of 



1 I am indebted to the kindness of Professor Mcintosh and Mr. John 

 Murray for the opportunity of examining the "Cliallenger" specimens of Cepha- 

 lodiscus, which has already been described by the former naturalist, but will 

 receive more ample treatment and illustration at his hands in one of the forth- 

 coming " Challenger" Reports. 



