The Morphology of Coeloplana. 69 
Fig. 9—13. Cellular elements floating in the circulating fluid of the 
canal system. 900:1. Fig. 9, 11 and 13 show the typical forms resulting 
from coalescence of several cells. Compare with figure 39, plate 5. 
Fig. 14. Cross section through skirt of C. mitsukurii near periphery. 
300:1. 4g. can cross section of a gastric canal. Note the contrast between 
the secreting and non-secreting portions of the endothelial lining. Between 
the epithelium and the canals is a loose parenchyma made up almost 
wholly of branched connective tissue cells. 
Fig. 15. Horizontal section (slightly tangential) through otolith 
capsule. C. willeyi. 160:1. cav cavity of the capsule, gl a few gland 
cells of the glandular zone, nv ganglia and nervous investment of the 
surface of the capsule, 7 cavity of the infundibulum which underlies the 
capsule and comes up about its sides. It is included in this section owing 
to the fact that the section is not cut quite horizontally. 
Fig. 16. ©. mitsukurü. Vertical section through a dorsal respiratory 
tentacle (quite strongly contracted). 365:1. ep dorsal epithelium, p. ¢ 
pigment cells of parenchyma, en endothelial lining of gastric canals, g. can 
diverticulum of gastric canal entering the tentacle and branching with it. 
Numerous cross sections of muscle bundles are to be seen in the parenchyma 
as well as numerous long independent muscle cells. 
Fig. 17—21. Cell elements of the parenchyma. 900:1. Fig. 17 
and 21; typical connective tissue cells with forked processes found where 
the parenchyma is loose and spongy (cf. Fig. 24). Figs. 18 and 20, 
connective tissue cells found in denser parenchyma; Fig. 20 is possibly a 
type of an early stage of development. Fig. 19 is a solitary muscle cell 
such as is found throughout the parenchyma. 
Fig. 22. Cell elements of the circulating fluid of the gastric canal 
system. 900:1. Division goes on after separation from the parent 
endothelium. 
Fig. 23. Phagocyte from tentacular sheath that has ingested portions 
of colloblasts. nucleus. 900: 1. 
Fig. 24. Ciliated epithelium of ventral surface of body. 300: 1 (ef. 
Fig. 7). The gland cells (gl. c) are in Stage B of the cycle, mb muscle 
bundle cut transversely, »n. ! layer of muscle cells immediately underlying 
the epithelium, ep» and separating it from the loose parenchyma. 
Plate 10. 
Fig. 25—31. Stages in the development of a colloblast (C. willey?). 
900:1. Fig. 25, 26, 27 are looked at from above, the rest from the 
side. Fig. 25, the undifferentiated cell. Fig. 26, the chromatin begins 
to aggregate into “nucleoli”. Fig. 26. These concentrate about the 
nucleus proper. Fig. 27. The cytoplasm begins to differentiate into a 
denser inner column and a spiral outer thickening. Fig. 28—29. The 
nucleoli have blocked off the cytoplasm about the nucleus into the typical 
mulberry shape, the central column has thinned and the spiral filament 
has become much more definite. Fig. 30, the typical spiral filament 
