474, RICHARD ASSHETON. 
being only very slightly less abundant than those which do not 
bear cilia. 
Ciliated cells occur more sparsely over all the rest of the 
sides, back, and ventral surfaces, and cause a steady flow of 
water, which is rather more rapid over the tail. 
The gill-filaments are provided with about one ciliated to 
every two non-ciliated cells (fig. 16). 
The ciliation after about the 7 to 8 mm. stage begins to 
become less effective. A tadpole of 6 or 7 mm. will progress, 
if placed upon its side in water along the bottom of a flat glass 
vessel, at the rate of one millimetre in from four to seven 
seconds. 
The Ciliation of the Later Stages of Larval Life. 
In tadpoles of 12 mm. in length, ciliated cells are still to be 
found on all parts of the body. The general flow is from 
before backwards. The motion is, however, much less rapid, 
and there are no longer any special currents. 
For instance, the streams connected with the cement-glands 
are now hardly distinguishable from the general flow. Areas 
wherein at an earlier stage every cell was ciliated, now contain 
many cells without cilia. 
The cement-glands have become much reduced. They are 
mere circular bosses. The high lateral ridges have entirely 
disappeared. Nor is the flow of secretion nearly as copious, 
and the tadpole makes but little use of it. . 
The action of the cilia now seems to be no more rapid along 
the dorsal surface than ventrally. 
The mouth and posterior nares are open, and the tadpole 
draws the water by muscular as well as by ciliary action into 
the pharynx by all three apertures. The exhalent flow by the 
opercular spout is extremely rapid and quite regular, and 
exhibits no signs of a muscular expulsion. 
At 18 mm. there is still a flow of water over the whole sur- 
face of the tadpole, but there are now regions which do not 
bear cilia. For instance, the fringe of tentacles which have 
grown round the lips of the mouth is quite destitute of cilia. 
