22 PENNATULIDA. 



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 Pom. phosphorca (and Renilla) 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 pohp itself being aborted. This Inpothesis would require so earh- an abortion of the terminal 

 polyp, that we know of no parallel in au}- other Pennatulid whatever. 



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

 to be denoted as the rtop-zooid . This interpretation would be met by a difficult)- 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 sa\-, at a \-er\- earl\- 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. p/iospJiorca, in which the terminal pohp seemed to have disappeared, a full grown 

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



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

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

 show quite a different interpretation to l^e 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 upjDer 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 evidenth- 

 stretches longitudinall) ; 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 

 fig.s. 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 ])art contains only the continuation of the longitudinal partition which farther down 

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

 point of separation, generalh- with a hook turned to the right but this ma>- also assume a somewhat 

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

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

 showing llie tran.sverse fi.s.sion belong to the large and middle-sized; the total length is between ca. 17 

 and 25"""; 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; >-et the largest specimen, with 7 pairs of wings, shows three individuals in wings II 

 and III: a large polyp, a quite small pohp and a zooid. De\-eloped sexual organs are found in some 

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

 to find them. Tlic jirocess 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 



