ON A FBEB-SWIMMING HYDHOID. 23 



Figs. 1 — 17 inclusive refer to the hydroid stage of Pelagohydra 

 niira bills; Figs. 18 — 25 inclusive refer to the medusoid stage of the same. 



Fig, 1. — The free-swimming hydroid, from a sketch of the living animal. 

 X 2. 



Fig. 2. — External view of a piece cut out of the preserved specimen, 

 showing tlie arrangement of the proboscis tentacles, etc. X 7. 



Fig. 3. — Three adjacent tentacles of the float, showing variation in shape, 

 from the preserved specimen. 



Fig. 4. — Portion of the surface of the float, much enlarged, showing the 

 stolons with the developing medusge, lying between the bases of the tentacles. 



Fig. 5. — The preserved specimen after removal of a portion of the wall, 

 showing the gastral cavity, septum, float cavity, supporting membranes of 

 float, endodermal canals, etc. x 4. 



Fig. 6. — Internal view of the piece represented in Fig. 2, showing septum, 

 longitudinal gastral ridges, endodermal canals, etc. X 7. 



Fig. 7. — Portion of the same turned so as to show the under surface of 

 the septum, with the annular fold of endoderm and the openings of the 

 endodermal canals into the main gastral cavity, x 7. 



Fig. 8. — Diagrammatic longitudinal section through a ))ortion of the wall, 

 showing the relations of the internal cavities, septum, endodermal canals, 

 supporting membranes, tentacles, stolon, medusa buds, etc. 



Fig. 9. — Part of a transverse section of the wall of the proboscis, through 

 the bases of the larger tentacles and the longitudinal gastral ridges of the 

 endoderm. Drawn under Zeiss objective A, oc. 2, camera outlines. 



Fig. 10. — Portion of a transverse section similar to and near the last, to 

 show especially the arrangement of the muscle-fibres. Drawn under Zeiss 

 objective D, oc. 2, camera outlines. 



Fig. 11. — Portion of a transverse section of one of the longitudinal gastral 

 ridges, showing the endodermal epithelial cells continued into muscle-fibres. 

 Drawn under Zeiss objective F, oc. 2. 



Fig. 12. — Part of a transverse section through the wall of the float, 

 showing an endodermal canal continued outwards into a stolon, and giving 

 rise to supporting membranes of the float by means of groups of cells budded 

 off from its lining epithelium. Drawn under Zeiss objective C, oc. 2, camera 

 outlines (slightly diagrammatic). 



Fig. 13. — Part of a transverse section of a supporting membrane from the 

 interior of the float, showing the mesoglceal layer covered on each side by a 

 syncytium, here collected on one side into a rounded multinucleate mass of 

 protoplasm. Drawn under Zeiss objective F, oc, 2, camera outlines. 



Fig. 14. — Surface view of one of the supporting membranes of the float. 



