144 DR A. MILNES MARSHALL ON THE 



The body of the polyp is greyish in colour, and from 10 to 15 mm. in length. 

 It is widest at its base— 4 mm. in the larger polyps, and gradually narrows in 

 its upper third to 25 mm. The upper part is marked by very distinct longi- 

 tudinal grooves opposite the septal attachments, and is also slightly corrugated 

 transversely. 



The tentacles are of a dark reddish-brown colour, and of about the same 

 length as the polyp body. Each is fringed by a double row of pinnules, which 

 exhibit an irregular alternation of larger and smaller ones (fig. 31); the larger 

 pinnules being inserted rather nearer the inner or oral surface of the tentacle 

 than the small ones. Lindahl* has directed special attention to this inequality 

 of the pinnules in the case of U. Lindahli (Koll.)t, where it appears to be much 

 more marked than in U. gracilis. 



The polyps and tentacles are non-retractile, or can at most be withdrawn to 

 a very slight extent, and there is no trace of a calyx. 



Structure of Polyp. — One of the polyps was removed for the sake of 

 studying its structure, and cut into a series of transverse sections. The 

 anatomy presents no points of special importance. The body wall is of only 

 moderate thickness, the body cavity and tentacular cavities being of large size. 

 As in Kophobelemnon the polyp cavities are prolonged into the rachis, but a 

 larger proportion of the polyp is free than in this genus ; the stomodseum and 

 upper part of the mesenterial filaments being contained within the free part of 

 the polyp, and the reproductive organs and lower part of the mesenterial fila- 

 ments being alone situated within the rachis. 



The plane of symmetry in the case of the one polyp examined, and pre- 

 sumably in the others as well, obeys the same laws that have been found above 

 to apply to Kophobelemnon and Pennatula, i.e., it is vertical and at right angles 

 to the surface of the rachis at the point of insertion of the polyp. The axial surface 

 of the polyp, moreover, is that which bears the two long mesenterial filaments. 



The single specimen obtained is a female, and the arrangement of the 

 reproductive organs is the same as in other Pennatulida, the ovaries being the 

 free edges of the six septa which bear, higher up, the six short mesenterial 

 filaments. Fig. 34 represents a section of one of these fertile septa and of the 

 part of the body wall from which it springs. The figure shows the largely 

 developed retractor muscle of the polyp rm, and at the edge of the septum ova 

 in various stages of development, each with a large nucleus and nucleolus, and 

 invested in a distinct epithelial capsule. The ripe ova have a diameter of 

 01 mm. 



* Lindahl, "Om Pennatulid-sliigtet Umbellula," Kongl. Svenska Vetenshaps-Altademiens Handling u r, 

 Bd. xiii. No. 3, Stockholm, 1874. 



t KoLLiKEit, Die Pennatulide Umbellula, Wurzburg, 1875. Kolliker proposes to group together 

 I.indaul's U. miniacea and U. pallida under the name U. lindahli. 



