PENNATULIDA. 83 



Unfortunately intermediate stages are wanting in my material between these young stages and 

 the large ones; but the break is filled, at all events partly, by the material of the Norwegian North- 

 Atlantic Expedition, which I have had the opportunity of seeing in the Bergen Museum. If we examine 

 the specimens described by Danielssen as Nrs. 2, 3, and 4, we shall find that besides the terminal polyp 

 and those representing the lower circle, 2 3 polyps are further found above the latter, which show 

 by their smaller size that they have only arisen recently; and in the specimens described by Danielssen 

 as Nr. 5 and 6, the polyps placed above the lower circle have increased in number and size, whilst at 

 the same time the number in the lower circle has increased; some of the specimens mentioned show 

 also that this latter increase is due to the fact that new rudiments of polyps arise in one certain 

 place in the lower circle, on the ventral side of the rhachis-club 1 ). The lower circle in all young 

 stages is really interrupted in two places, viz. at the dorsal side of the colony where the rhachis-club 

 with its dorsal belt of zooids reaches to the base of the terminal polyp, and on the opposite side 

 where the rudiments arise; in other words: the lower circle is formed of two lateral rows, a right 

 and a left, corresponding to the two lateral rows of polyps which are placed along the dorsal side of 

 the rhachis in sea-pens of the common long form; as in such forms the polyp in each of the two 

 rows which is placed nearest to the terminal polyp (uppermost) is the oldest one, the polyp placed 

 farthest therefrom (lowermost) the youngest such is also the case here in Umbellula. 



My two young Umb. encrinus (Nr. i and 2) in spite of their considerable size thus represent 

 just the stage which in Virgularia I have called the Profocaulon-stage, and the stage which I have 

 formerly described and figured for Pennatula phosphorea (Vid. Medd. Nath. For. Kbhvn. 1888). This is 

 also seen quite easily and convincingly, if we take into the comparison such Umbellula-sp&cizs where 

 the rhachis-club is more elongated, e. g. U. gilnthe.ri (partly U. leptocaulis, simplex, and carpcnteri). 

 The other polyps, which arise inside (above) the lower circle, must then of necessity correspond to 

 those placed on the ventral surface of the rhachis in other sea-pens, which is bordered by the two 

 dorso-lateral rows of polyps; accordingly, they correspond to the polyps which in most sea-pens are 

 arranged in oblique rows. Now the appearance and arrangement of these polyps is irregular in 

 several sea-pens (as in Anthoptilum murrayi, the species of the genus Kophobelemnon a. o.); sometimes 

 not even a grouping on either side of the ventral median line is preserved. In Umbellula encrinus 

 the case is as in these latter; at all events, I have not been able to find any invariable regularity in 

 the appearance and arrangement of the upper or inner polyps. So much is evident, however, that 

 Umbellula like the typical Pennatulids has two regions of growth where new individuals arise: one 

 corresponding to that where, in forms with wings (as a Pennatula\ new wings arise, and one corre- 

 sponding to that where the number of individuals in the wings increases. And as in all other bilateral 

 sea-pens those polyps are largest which form the two most dorsal longitudinal rows, so in Umbellula 

 the corresponding polyps, i. e. those of the lower circle, are the largest. 



In large specimens of Umb. encrinus the polyp-cluster appears to be radiate; but a closer inspec- 

 tion of the tongues of zooids will show that the bilateral structure is preserved in reality. The fact 

 is that one of these zooid-areas is always a little larger than all the others, especially somewhat 



r ) This cannot be seen from the figures of Danielssen or be gathered from his text; in some of these specimens he 

 has overlooked the rudiments or not mentioned them. 



