CILIATION OF ECTODERM OF AMPHIBIAN EMBRYO. 483 
Fie. 2,—A few hours later than Fig. 1. The cross indicates the furthest 
point backwards upon which cilia may be present. 
Fic. 3.—A slightly older stage. In this a second area of ciliation has 
appeared, as indicated by the arrows, along the antero-ventral surface. 
Fic. 4.—Embryo of frog, showing current along the dorsal groove formed 
by the junction of the neural folds. 
Fig. 5.—Embryo of frog, about 3 mm. long. The whole surface is now 
ciliated, although ventrally the ciliation is very scanty. Three well-marked 
streams are indicated by the arrows V.BC., SC., and CC., respectively. 
Fic. 6.—Diagram showing the currents of water produced by the ciliation 
about the region of the blastopore and anus. 
Fie. 7.—Diagram showing the currents of water produced by the ciliation 
at the posterior end of the embryo, after the closure of the blastopore and 
growth of the tail. 
Fic. 8.—A semi-diagrammatic figure of a transverse section across the so- 
called sucker of the frog embryo of about 63—7 mm. ‘The epidermic layer of 
epiblast, #P.#., is a layer of one cell in thickness, which cells at two points, 
C.GL., become enormously lengthened, and secrete a very sticky kind of 
mucus. The neighbouring cells bear cilia. Those upon the walls of the 
ridges nearest the cement or mucus-secreting glands bear very short 
cilia; those more remote, and especially those between the two bases, bear 
very long cilia. Hach long mucous gland-cell is broad at its base, contains 
a large nucleus surrounded by “granular” protoplasm at that part, and 
narrows into a long neck as it reaches the surface, filled with the sticky 
secretion, which stains slightly with most stains, but with plain hematoxylin 
it stains deeply. 
Fie. 9.—A semi-diagrammatic figure of the “sucker” at a rather later 
stage, namely, a tadpole 8—9 mm. in length. In this the ridges bounding 
the glands are much more prominent. In reality the gland-cells lie diagonally 
from before backwards, so that their necks and openings are much more 
posteriorly situated than their protoplasmic bases. 
Fie. 10.—Ventral view of a 34-mm. tadpole, showing the currents of water 
produced by the ciliation of the ectoderm. 
Fic. 11.—Ventral view of a 6-mm. tadpole. The arrows indicate the 
general flow of water and the special streams on the ventral surface. 
Fig. 12.—Lateral view of the same embryo as preceding. 
Fic. 13.—Ventral view of anterior end of an $-mm., tadpole. The arrows 
indicate the main currents produced by the special ciliation connected with 
the stomodeum, the mucous glands and olfactory epithelium, and branchial 
filaments. 
Fig. 14.—Side view of the same embryo as preceding. 
