22 PENNATUUDA. 



of the polyps in question, partly because both the upper polyps (I) always (or, at all events, with 

 very rare exceptions) distinctly appear as lateral polyps, i. e. wing-polyps, a polyp Nr. 2 sometimes even 

 a Nr. 3 being found at their base on the ventral side of the colony (whether these latter ever grow- 

 to their full size is of no consequence in this connection); in Penn. phosphorea (and Renilld) the term- 

 inal polyp is always single, and continues to be so. 



2) The large zooid on the end of the rhachis might be interpreted as the terminal zooid, the 

 terminal polyp itself being aborted. This hypothesis would require so early an abortion of the terminal 

 polyp, that we know of no parallel in any other Pennatulid whatever. 



3) The terminal polyp might be transformed into the large zooid, which ought, in this case, 

 to be denoted as the top-zooid . This interpretation would be met by a difficulty quite similar to 

 the one in supposition Nr. 2, and further by the fact that the original terminal zooid must have dis- 

 appeared at the same time — that is to say, at a very early stage. This seems little probable, when 

 it is remembered that v. Koch has in one case found the real terminal zooid to be preserved in a 

 specimen of P. phosphorea, in which the terminal polyp seemed to have disappeared, a full grown 

 specimen with 38 pairs of wings (comp. v. Koch, 2, p. 397, fig. Y). 



Although, in spite of the difficulties indicated, the possibility is scarcely quite rejected that one 

 of the two latter suppositions, or both, may apply to this species, I believe I have observations which 

 show quite a different interpretation to be the correct one, and make the others superfluous. 



The fact is that amongst the many specimens from St. 36 no less than 18 individuals, and 3 

 individuals amongst those from St. 24, show that this species is capable of transverse fission. By this 

 fission only the upper end of the rhachis with the uppermost pair of wings (I) is separated. The 

 separation always take place close above the second uppermost pair of wings (II), and before it is 

 quite accomplished the part of the rhachis situated between the two uppermost pairs of wings evidently 

 stretches longitudinallv ; by this means, the part prepared for separation becomes similar to the 

 the youngest known stages of development described above; compare figs. 19, 20 with the top of 

 figs. 21 and 22. A clearing with glycerine or oil of cloves shows, however, that all the specimens in 

 hand which are in the act of transverse fission, contain no calcareous axis in the top-part destined for 

 separation; this part contains only the continuation of the longitudinal partition which farther down 

 in the rhachis contains the calcareous axis. This axis itself terminates always immediately below the 

 point of separation, generally with a hook turned to the right but this may also assume a somewhat 

 different form (comp. fig. 22). This want of an interior calcareous axis is literally the only difference 

 that can be pointed out between the top and one of the youngest independent colonies. The specimens 

 showing the transverse fission belong to the large and middle-sized; the total length is between ca. 17 

 and 25" ln, ; the number of wings is 4 pairs with 2 or 3 pairs of rudiments, and up to 7 pairs and 3 

 pairs of rudiments; each wing is generally provided with two individuals, of which Nr. 2 is almost 

 always a zooid; yet the largest specimen, with 7 pairs of wings, shows three individuals in wings II 

 and III: a large polyp, a quite small polyp and a zooid. Developed sexual organs are found in some 

 of the specimens, but in several others, e. g. the one represented in fig. 21, I have not been able 

 to find them. The process of transverse fission itself is seen in somewhat different stages; where the 

 constriction of the rhachis is not deep, the top is least lengthened (comp. fig. 23); where the constriction 



