4.72 RICHARD ASSHETON. 
ridges. A small portion passes straight on, making a stream 
which becomes very prominent a little later. 
When the tadpole measures about 8 mm. the cement-glands 
are at their greatest development. Fig. 13 is a ventral view 
of this stage. 
The two glands appear as though raised upon a horseshoe- 
shaped platform. Each gland, which is elongated in an antero- 
posterior direction, is bordered on both sides by a high ridge 
richly ciliated (fig. 9). The shape of these ridges and direc- 
tion of action of the cilia upon them is such as to produce the 
following currents in the adjoining water, as indicated by the 
arrows in fig. 13. 
(i) Externally, strong currents, C.C., which skirt round the 
ridge towards the mid-ventral line. 
(ii) Centrally, a strong stream, S.C. (the deeper portion of 
which passes first into the stomodzal cavity, in which particles 
may be seen to revolve in eddies for some minutes), runs up 
the groove from the stomodeeal depression, and turns over the 
hinder border of the inner ridges of the glands, and drives the 
water in a strong stream partly straight outwards and away 
from the larva, and partly along the ventral surface (vide fig. 14) ; 
the effect being to sweep clean the hinder part of the glands. 
(iii) The cilia on the crests of the ridges and on the sides of 
the ridges facing the glandular cells cause water to be drawn 
into the glands, which sweeps any secretion from the gland 
backwards until it comes into the very strong stream described 
last. These currents are indicated by the small arrows in 
fig. 13. 
When the tadpole first leaves the egg membrane, and 
wriggles or is driven outwards from the jelly mass by the 
action of its cilia, it may perhaps be said to adhere to the jelly 
by suction, for the jelly is sufficiently fluid to be drawn into 
the hollow of the glands by the currents of water over the 
ridges, and too viscid to pass easily through and out again. 
But suction plays no part at all in the mode of adhesion to any 
object of a more rigid nature, such as a plant leaf, piece of 
root or stick. The tadpole is seen to be anchored by the sticky 
