MUSEUM OF COMPARATIVE ZOOLOGY. 9 



just described for Urnatella has been described and figured by Ehlers 

 for Ascopodaria. Such a highly complicated septum seems indeed 

 to be common to the Pedicellinidtc, which in this respect appear more 

 nearly allied to Urnatella tlian does Loxosoma, in which such septa are 

 absent. 



In Pedicellina Benedeni also, which has a segmented stalk, the seg- 

 ments are separated from one another, according to Foettinger ('87, 

 pp. 301-303), by perforated septa. 



2. The Calyx. 



Under this heading I shall treat successively of the body wall (includ- 

 ing the lip of the atrium, and the tentacles), the atrium, the alimentary 

 tract, the body cavity, the nephridia, the sexual organs, and the nervous 

 system. 



A good idea of the external form of the expanded calyx may be gained 

 from Leidy's figures. My own, having been drawn chiefly from preserved 

 material, show the polypide for the most part in a retracted condition 

 (cf. Plate T. Fig. 2). When thus retracted, the atrial opening does not 

 lie at the apex of the calyx, but is thrown sharply over towards the oral 

 aspect (Plate III. Fig 18). 



The body wall is composed of a single layer of excessively thin epi- 

 thelium, — the ectoderm, — which has secreted a thin cuticula. This 

 cuticula is thickened in places, producing papillae, which are irregularly 

 scattered over the calyx. At the lip of the atrial opening, as the pas- 

 sage into the atrium in the retracted condition may be called, the ecto- 

 derm is thicker than elsewhere, and folds back upon itself until it reaches 

 the base of the lophophore. This backward-reflected portion I shall 

 call by the name Jcamptoderm, for although its homology with the kamp- 

 toderm of Ectoprocta may not be entirely beyond doubt, I cannot -see 

 any important difference between the two structures, either in their adult 

 relations or in development. As in the Ectoprocta, so here the polypide 

 is formed in the retracted state, and the atrial opening does not break 

 through until a late stage is reached. 



In Ectoprocta the line of union of the kamptoderm and body wall, 

 i. e. the lip of the atrial opening, is marked by a thickened ring com- 

 posed of elongated ectodermal cells, at the base of which lie the fibres of 

 a sphincter muscle. This organ constitutes the " Ptandwnlst " of Phy- 

 lactolsemata or the " Diaphragma " of Gymnolsemata. Does an organ 

 homologous with this occur in Urnatella 1 It is in keeping with the 

 more primitive organization of the Endoprocta that, although a corre- 



