386 ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
I. 1. II. Iv. v. Segments of the blastoderm. 1. Cyathozooid. 11.-v. Ascidiozooids . 
I, 2, 3, 4, isthmuses. 
B, the mouth of the cyathozooid, as formed by the test, and which becomes the future lip or 
‘sphincter’ of the cloacal aperture ; 8', aperture of the cyathozooid when separated 
from the foregoing. 
y, cavity of the cyathozooid. 
5, appendix of the cyathozooid. 
6, canal connecting the first isthmus with the cavity of the cyathozooid. 
PLATE XXX. [PLATE 29]. 
Fig. 1. A side view of a single ascidiozooid from the middle of the ascidiarium of Pyrosoma 
giganteum. 
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, peripharyn- 
geal ridge, ganglia, and anterior end of the endostyle. There are more vascular 
bands (73) 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 ¢ lie altogether above the intestine, and hence 
do not interrupt the communication between / and #} 1. 
Fig. 4. A vertical section of the wall of the ascidiarium, near the cloacal aperture and includ- 
ing 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 & 7a. The atrial aperture viewed under the same aspects. 
Fig. 8. A transverse and vertical section of the middle of the hzmal 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. /# indicates 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 cut, 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, 77. 
Fig. 25. A bud so far advanced as to be connected with the cloaca by its atrial aperture, 2°. 
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 hzemal side. 
Fig. 30. A still more advanced bud viewed from the hzmal side, and given partly in section, 
to compare with fig. 3. 
