Plate III. 



Fig. I. Embryo in the stage III. The skin of the one side removed so as to show the tentacular sheaths; 

 below these are seen the two entodermal sacs of the under side, those of the upper side 

 having been removed. +°/'i. 



— 2. The aboral region, with the costse and tentacles, of an embryo in the Stage III. The skin 



folds over the costse have been omitted, being indistinct in the flattened preparation. The 

 left tentacle sheath was torn away and is therefore not represented in the figure. From the 

 aboral organ are seen the ciliated ridges going to the costse. ss/^. 



— 3. Young specimen, after leaving the egg-membrane. The costse have disappeared. The edges of 



the transversal furrow have united at the right side, the secondary mouth-opening having thus 

 been formed; the upward growth of the secondary mouth-opening has also begiui, though 

 there is as yet no distinct "chimney". The skin of the side turning towards the spectator 

 has been prepared away so as to show the branching of the entodermal sacs — the begin- 

 ning of the branching peripheral canal system of the grown specimens. -7/,. 



— 4. Embryo in Stage III, corresponding to that figured in fig. i. — The skin partially removed 



so as to show the pharynx and the entodermal sacs, but the costae have been left in 

 place. The tentacles are seen rolled up within the tentacle sheath; the right tentacle is seen 

 to protrude a little into the transverse furrow, -ts/i- 



— 5. Part of the basal surface of a grown specimen; the furrow closed. (Comp. Fig. 11). ^/i. 



— 6. Embryo in Stage III, with the lobes spread out horizontally; seen from above. The skin 



has been removed so as to expose the entodermal sacs and the tentacle bases and sheaths. 

 In the middle the skin remains, the aboral organ and the costse lying in place. ^5/,. (The 

 oesophagus was indistinct in the preparation and has therefore not been indicated in the 

 figure). 



— 7. Part of the side wall of a "chimney" seen from the inside, showing the folding of the skin. 



The opening of the tentacle-sheath is seen; above the tentacle-base are seen the genital 

 organs of the side looking towards the spectator, turned upwards, and below these part of 

 the stomodccal folds are seen. '7/j. 



— 8. Embryo in Stage II; the skin partly removed so as to show the configuration of the oeso- 



phagus and the invaginated portion of the transverse furrow. The interior was filled by 

 a mass of large entoderm cells, but the exact relations of these and the existence of entodermal 

 cavities could not be made out, owing to the — for this purpose — unsatisfactory preserv- 

 ation. Side view from the sagittal plane. 5^/,. 



— 9. Regenerating half of a grown specimen, showing the relations of the genital organs and the 



branching peripheral canal system to the main transverse canal (the perradial vessel). 

 The epidermis has been removed. Side view, a little obliquely. The genital organs of the 

 side away from the spectator pushed a little upwards so as to become visible, ^s/i . 



— 10. Tentacle and tentacle basis, seen from the apical side, of a young (regenerated) specimen. 



The small genital organs (only the subtentacular pair drawn) are seen to develop at the end 

 of small branches from the tranverse canal, ^s/j. (Comp. Fig. 12). 



— II. The basal surface of a grown .specimen. The furrow ("suboral" cavity) is opened so as to show 



the large stomodseal folds, in the middle of which is seen the narrow opening of the oeso- 

 phagus (in the figure designated o). The hole (o. f.) at each end of the furrow represents the 

 opening from the furrow into the lumen of the "chimneys", ^i • (Comp. Fig. 5). 



— 12. Tentacle and tentacle basis of a grown specimen, seen from the outer side. The small 



finger-shaped body at the base of the tentacle probably represents a secondary (abnormal) 

 tentacle. (Comp. Fig. 10). The two large bodies lying over the tentacle basis are the two 

 subtentacular genital organs, -s/j. 



