AND DEVELOPMENT OF PYROSOMA. 249 



Plate XXX. 



Fig. 1. A side view of a single ascidiozooid from the middle of the ascidiarium oi Pyrosoma (j'ujanteum. 



Fig. 2. A transverse and vertical section of the middle of the branchial region of a similar ascidiozooid, 

 exhibiting, in addition, the oral aperture, anterior muscles, peripharyngeal ridge, ganglia, and 

 anterior end of the endostyle. There are more vascular bands (j-^) represented than would be 

 seen in any one transverse section. 



Fig. 3. A transverse and horizontal section of an ascidiozooid without any labial process. It should be 

 understood that s and t he altogether above the intestine, and hence do not interrupt the 

 communication between p and jo' />'. 



Fig. 4. A vertical section of the wall of the ascidiarium, near the cloacal aperture and including its lip. 



Fig. 5. View of part of the closed end of the ascidiarium, showing the four ascidiozooids (* * * *) which 

 form its apex. 



Figs. 6 & 6a. The oral aperture viewed from within and from the side. 



Figs. 7 & 7«' The atrial aperture viewed under the same aspects. 



Fig. 8. A transverse and vertical section of the middle of the haemal region of the branchial sac, showing 

 the endostyle and the parts adjacent. 



Fig. 9. Part of the wall of the middle of the ascidiarium viewed from within, or from the cloacal side. 



Fig. 10. The cloacal fibrillated layer. 



Fig. 11. A cell of the general substance of the test. 



Fig, 12. The nervous ganglion viewed from above. 



Fig. 13. A section of the body- wall of an adult ascidiozooid, taken through the 'urinary' organ, l'^ indi- 

 cates a minute depression which I was at one time inclined to regard as an aperture into the 

 parietal sinus over this organ ; but I suspect it is only a nascent stigma. 



Fig. 14. The youngest condition of a bud, before the external tunic is elevated. 



Figs. 15-20. Successive stages of development of the buds, described in the text. 



Fig. 21. A bud laid open by a vertical ctit, and exhibiting an interior view of the branchial sac. 



Fig. 22. A more advanced bud, with a second bud forming in its peduncle. 



Fig. 23. A still more advanced terminal bud, a second median bud in about the same stage as fig. 20, 

 and a third proximal bud developing in the peduncle and nearly in the same stage as fig. 17, 

 all connected together. 



Fig. 24. A bud naturally detached from its peduncle, and exhibiting a rudiment of the stolon, r^. 



Fig. 25. A bud so far advanced as to be connected with the cloaca by its atrial aperture, j3-. 



Figs. 26 & 27. Very young buds, viewed from the side to which their apices are turned. 



Figs. 28 & 29. More advanced buds viewed from the haemal side. 



Fig. 30. A still more advanced bud viewed from the haemal side, and given partly in section, to compare 

 with fig. 3. 



Plate XXXI. 



Figs. 1, 2, 3 & 4. Ovisacs containing complete ova in different stages of development. The fraction 



above each figure gives the greatest diameter in parts of an inch. 

 Fig. 5. An ovisac, torn at one point, but otherwise entire, and allowing the naked germinal vesicle to be 



seen through its wall. 

 Fig. 6. A similar ovisac opened with needles, and the torn lower portion, to which the germinal vesicle 



adheres, viewed from within. 

 Fig. 6 a. An enlarged view of the germinal vesicle. 

 Fig. 6 6. A similarly magnified view of the dilated end of the duct of the same specimen, showing the 



' plug ' of spermatozoa. 

 VOL. XXIII. 2 L 



