410 E. W. MACBRIDE. 
Fie. 136.—Section of the adhesive disc of larva shown in Plate 21, figs. 
62—69. wz. A small piece of alga, to which it adheres by a secretion of 
mucus. ist. Involutions of neighbouring portions of ectoderm to undergo 
destruction by amcebocytes, ameb.; by this means the preoral lobe is reduced 
in size. Magnified 480 diameters. 
Fic. 187.—Section of the lateral wall of preoral lobe of larva of Stage D. 
musc. larv. Larval muscles derived from the peritoneal cells. Magnified 1000 
diameters. 
Fic. 188.—Section through the ectoderm and hydroccele wall of a larva of 
Stage D, to show the characters of the various larval epithelia. Magnified 
1000 diameters. 
Fie. 139.—Similar section from a larva between Stages EH and F. A peri- 
hemal rudiment is shown. Magnified 1000 diameters. 
PLATE 28. 
Figs. 148, 149, and 150 are magnified 600 diameters, the rest 1000 dia- 
meters (Leitz’s immersion 35). 
Fic. 140.—Similar section from a larva of Stage F (that shown in Figs. 
62—69). mxerv. The incipient nervous tissue developing as a fine plexus 
amidst the bases of the ectoderm cells. 
Fic. 141.—Similar section from a young star-fish, in which R equals 
‘4 millimetre. Nerv. circ. Nervous ring. calc. Calcigenous tissue. jibr. 
Fibrous tissue. re¢r. musc. Retractor muscles of stomach. 
Fie. 142.—Developing eye of same star-fish. A simple ectodermic pit is 
seen. 
Fic. 143.—Eye of star-fish from which Figs. 129—182 are taken. ret. 
Visual cells. vit. Cells functioning as ‘ Glaskorper.” 
Fics. 144—148 illustrate the differentiation of tissues in the body-wall. 
Fig. 144. From the right side of a larvaof Stage D. At * a cell is 
seen in the act of dividing, to form one of the amebocytes of the 
ccelom. 
Fig. 145. From larva of Stage E (that shown in Figs 51—53). god. 
Goblet cells. mzasc. Developing muscles; as yet they are simply tails 
of the celomic epithelium. jidr. First rudiment of fibrous tissue. 
Fig. 146. From the young star-fish from which Fig. 141 is taken 
calc, Small portion of calcigenous tissue. 
Fig. 147. From the young star-fish from which Fig, 148 is taken, and 
also Figs. 129—182. 
Fig. 148. Ectoderm of another specimen of same age, to show the sense- 
cells. 
Fic. 149.—Tube-foot of the larva shown in Figs. 62—69. 
Fic. 150.—Tube-foot of the star-fish from which Figs. 141 and 146 are 
