PENNATULIDA. 31 



the developmental stages known of P. pliospliorea renders it quite untenable. Penn. phosphorea 

 always shows more numerous and more advanced polyps in the single wings, at stages where the 

 number of wings is as in specimens of the present new species, and the colony is upon the whole 

 more developed at corresponding sizes; on the other hand, the young colonies of P. phosphorra show 

 no ripe sexual organs. These features, however, might be thought to be influenced bv the conditions 

 of life at such great depths as the one from which the new form has been obtained. The most con- 

 clusive thing to my mind, howe\er, is the great difference in the construction of the )ipper end of 

 the rhachis. In young colonies of Pcnn. phosphorea the rhachis always terminates above in a terminal 

 polyp, and on the dorsal calyx-base of this there is a large terminal zooid which completes the rows 

 of dorsal zooids'). Both terminal polyp and terminal zooid are found even in well-developed colonies 

 with complete pen-form (for instance, in specimens of more than 35""", with 12 pairs of wings, the 

 largest of which are provided with 5 — 6 polyps; but more rarely in still larger specimens); in the new 

 species however, no stage not even the youngest, shows the least indication of a terminal polyp: the 

 rhachis ends as stated in a large zooid, and the two nearest polyps (or wings) are equallv developed 

 and placed at almost the same height; thus the younger stages especially have a dichotomous appea- 

 rance, markedly different from that of Penn. phosphorea. 



According to what has been known hitherto, the primar\- individual, developing directl\- from 

 the larva which arises from the Qgg^ is in all Pennatulids a polyp with tentacles (see my treatise 

 pp. 162, 173); as this polyj) grows greatly in length, its lowermost part below the calyx forms the 

 stem (rhachis -|- peduncle); on this lengthened part the other individuals, polj-ps and zooids, appear 

 gradually (in some genera zooids are also formed on the polyps). During the growth of the colonv 

 the terminal polyp may later disappear; this is probably the case in most of the genera of sea-pens, 

 and it is the rule in Peim. phosphorea. Where the disappearance of the terminal polyp is not due to 

 a mere displacement (as in Kophobelemnon), it may be due either to an abortion or a transforma- 

 tion into a zooid. In the genus Pteroeides the latter seems to be the case; when the colony has 

 grown to a certain size, the end of the axis, at all events, carries a ver}' large zooid instead of a ter- 

 minal polyp, (see Kolliker, Monograph, p. 356, my previous treatise, p. 172, and v. Koch 2, p. 398). In 

 Penn. phosphorea.^ the end of the rhachis of large colonies carries generally several very large zooids 

 «top-zooids» ; amongst these presimiably, are both the original terminal zooid and — by a retrograde 

 transformation — the terminal polyp and some of the uppermost wing-polyps (comp. Juugersen p. 168, 

 and V. Koch). With these facts in view we return to our new Pennahcla-s^&c\&s. It may be main- 

 tained with a probability, bordering on certainty, that this species like P. phosphorea, has also had a 

 stage not only with a terminal polyp, but also with a terminal zooid on its calyx-base. — I shall only 

 recall the fact that such a distant form as Renilla agrees completely in this respect with P. phosphorea. 

 How, then, has the terminal polyp disappeared here? 



i) If a displacement had been the cause, one of the two uppermost polyps would have to be 

 regarded as the terminal polyp, and the large zooid of the end of the axis would represent the terminal 

 zooid. This supposition, however, is inadmissible, partly because this large zooid is not placed in the 

 same way as the real terminal zooid in P. pJiosphorea and Renilla, on the dorsal calyx-base of either 



>J Comp. my previous treatise p. 16S, and Marshall & Fowler, Penn. «Porcupine., PI. XXXII, figs. 5 and 7. 



