PENNATULIDA DREDGED BY H.M.S. " TRITON." 149 



This extraordinary profusion mark the locality as a very exceptional one. 

 At each of the other stations only single species were obtained. 



Vertical Distribution. — The " Triton " observations have increased the ver- 

 tical range of Pennatula phosphorea to 555 fathoms, its previously recorded 

 limit being 340 fathoms ; of Diibenia abyssicola, from 120 to 555 fathoms ; of 

 Kophobelemnon stelliferum v. durum, from 300 to 640 fathoms ; and have added 

 a new deep water Virgularia, V. tuberculata, extending to 555 fathoms, to the 

 sole one previously known, V. bromleyi. 



These results, so far as they go, do not lend any very material support to 

 Kolliker's conclusion, that " the simpler forms of Pennatulida, especially those 

 with sessile polyps, inhabit great depths.""" 



Kolliker ranks among primitive forms of Pennatulida the Umbettulidw, 

 which are an essentially deep water family, seven out of the twelve known 

 species being found below 1000 fathoms and five below 1800 fathoms, and cites 

 this distribution in evidence of the view that the lower forms of Pennatulida 

 are, as a rule, deep water forms. 



Umbellula appears to me, however, to be not a primitive form but a highly 

 modified one. This is shown by the great length of the non-polypiferous as 

 compared with the polyp-bearing part of the colony, i.e., the great prepon- 

 derance of the purely colonial portion ; by the great difference between the 

 polyps and the zooids ; by the extreme differentiation of some of the zooids ; 

 and, above all, by the polymorphism of the zooids themselves, an almost unique 

 condition among Pennatulids. In all these respects Umbellula is far less pri- 

 mitive than Funiculina, which is essentially a shallow water form, attaining its 

 maximum of development at about 30 fathoms depth. 



A point of considerable interest concerns the influence of increase in depth on 

 the structure and habits of Pennatulids. On this point but little can be said at 

 present for want of sufficient evidence. 



We have seen above that some of the deep water forms (below 500 fathoms) 

 have much thicker body walls and layers, and more numerous spicules, than 

 those from less depths. If we compare different genera together there would 

 appear to be no relation whatever between depth of water and development of 

 spicules ; thus Umbellula gracilis and Virgularia tuberculata from 555 fathoms 

 have no spicules at all ; while P. phosphorea and K. stelliferum, brought up in 

 the same dredge with the preceding species, have exceptionally large and 

 numerous spicules. If, however, we confine ourselves to one species, we seem 

 to find such a relation ; thus the specimens of Pennatula phosphorea from below 

 500 fathoms have very much thicker walls, and larger and more abundant 

 spicules, than those from 20 to 40 fathoms. In this case we have strong reason 



* Kolliker, Zool. Chall. Exp., part ii. 1880, p. 39. 



