PENNATULIDA DREDGED BY H.M.S. "TRITON." 131 



the polyps, especially the simultaneous appearance of the component polyps of 

 a group ; by the position of the reproductive organs in the immature polyps, 

 the proportions of the stem at different heights, and by the existence of such 

 forms as Virgularia bromleyi * in which the separation of the polyps is not 

 carried quite so far as in V. tuberculata. From V. bromleyi, the new species is 

 distinguished at once by the absence of calcareous spicules, and the presence of 

 the tubercles marking the calyx margin. 



Concerning the development of the polyps, it can be ascertained by examina- 

 tion of the immature polyps at the lower end of the rachis, that the stomodasum 

 arises as usual as an involution of the ectoderm, appearing before the tentacles, 

 which latter all develop simultaneously. In the early stages of development one 

 tentacle is very commonly rather larger than the other seven, but whether this 

 is an accidental feature or not I have been unable to determine, nor have I 

 detected any constancy of position of the larger tentacle. In each group 

 the ventral polyp is always the furthest developed, and the dorsal one the 

 least so. 



In the smaller of the two specimens in which the stalk is perfect, the 

 change from the immature to the fully developed polyps is a very abrupt one ; 

 not gradual as in the larger specimen figured (PL XXI. fig. 1). The stalk in this 

 smaller specimen is 8 mm. long ; the first 4 mm. of the rachis bear immature 

 leaves only, and above this point the fully formed polyps commence abruptly. 



The fully expanded polyp (fig. 2) measures about 2 5 mm. in length, of 

 which the tentacles form rather more than half; its width is about 0*2 mm. 

 Opposite the insertion of the polyp, and for some little distance above and 

 below it, the sarcosoma of the rachis is markedly thickened (fig. 2), giving the 

 rachis at these places a quadrangular shape. The boundary line between the 

 body of the polyp and the tentacles is indicated in the fully expanded polyp by 

 a row of eight small knob-like processes placed opposite the tentacles (fig. 2). 

 These processes are hollow, and consist of all three layers of the body wall — 

 ectoderm, mesoderm, and endoderm ; they appear to correspond to the calyx 

 processes of other Pennatulida. 



When the polyp is retracted, as in the lower specimens of fig. 2, these pro- 

 cesses mark the line of invagination, and become much more consjDicuous, 

 appearing as knobs placed round the edge of the calyx. 



In the " Triton " specimens, retraction of the polyp is never carried further 

 than is shown in fig. 2, the fully retracted polyp being about half the length of 

 the fully expanded one. Eetraction is probably effected slowly, as the great 

 majority of polyps have died in an almost completely expanded state. 



The tentacles are rather longer than the body of the polyp ; are pinnated as 

 shown in fig. 2, and present no special features of importance. 



* Kolliker, Zool. Chall. Exp., part ii. p. 9, 1880. 



