Plate III. 



Figures i — 6 Ptychogena lactea A. Agassiz. 



Figure i. Dorsal wall of the stomach seen from the inner side, showing the four grooves, which in 

 this specimen do not meet exactly in the centre. The margins of the grooves are developed 

 into lateral, longitudinal folds, which transform the grooves into closed canals, which open 

 into the stomach near the centre; these openings are seen in the figure. — From a speci- 

 men, 90 mm wide, from "Tjalfe" stat. 125. — x 3. 



— 2. Transverse section of a radial canal with two lamellse with their papillse. The lower part 



of the figure represents the funnel-shaped, ventral part of the radial canal, separated from 

 the narrow, dorsal part by the two longitudinal folds, which are clearly visible in the figure. 



— From the same specimen. — x 6. 



— 3. Part of the conical part of a radial canal. The ventral wall is partly cut away, so that the 



longitudinal folds, which separate this part from the narrow, dorsal part, are visible. — 

 From the same specimen. — x 6. 



— 4. Longitudinal section through a part of a radial canal, showing the entrances to the lateral 



pouches, the longitudinal fold, and the lateral wall of the funnel-shaped part of the canal. 



— From the same specimen. — x 6. 



— 5. Transverse section through four of the lamellse (parallel with the radial canal) with male 



gonads. In the second lamella from the right the section has passed through the middle of 

 one of the papillse, demonstrating that the lumen of the latter communicates with the lumen 

 of the lamella. In the first lamella from the right the section has touched one of the pa- 

 pillse. In the papillse the entoderm consists of a single layer of cubical cells; in the lamellae 

 there are several layers of smaller entodermal cells. — Microtome-section. — From the same 

 specimen. — x 20. 



— 6. Radial section through the bell-margin, showing a tentacle and a cord}lus. On the abaxial 



side of the base of the tentacle is seen the .short conical extension, the rudimentary spur. 

 The cordylus is mounted upon a small tubercle. — From a sjjecimen from Lat. 59°07' N., 

 Long. i3°32' W. One of the type-specimens of Ptycltogciia piiniiihita Hat-ckel. — x 17. 



— 7 a — f. Sfaurop/iora mertcnsii Brandt. — Examples of cordyli developing into tentacles (see 



p. 6 in the text). — From a specimep from Iceland, "Thor" stat. 208 (04). — x 20. 



— 8. MelicertiiDi octocnstatitDi (M. Sars). — Transverse section through a radial canal with female 



gonads. Showing the broad line of attachment to the subumbrella and the considerable 

 distance from the subumbrella to the upper edge of the gonads. — From a specimen from 

 Iceland, "Thor" stat. 258 (04). — x 50. 



