The Plathander'' (Xenopus laevis). 
353 
The pharynx (Fig. 7) is more or less triangular in outline when looked 
at from above or below ; the one point is anterior the other two postero- 
lateral. The whole cavity of the pharynx is continuous ; the gill-slits are 
really giW-pouches in the floor of the pharynx; these pouches" are long 
narrow grooves of which there are three pairs, the anterior pair being the 
longest, the posterior pair the shortest. The grooves are supported by 
bars of cartilage lying between them and sending branches to their 
ventral floors. The lumen of each groove is much reduced by a fold 
of skin from the roof of the pharynx which grows down and causes 
7. — Schematic dorsal view of pharynx (from reconstruction of serial sections). 
M = mouth cavity; St ^ stomach ; Ph = central canal of pharynx; 1, 2, 3 = grooves in 
floor of pharynx separated from each other by ridges a, b, c, 4 = opening of lungs. 
OE = opening to exterior (see text). 
the gill-grooves to be V-shaped in section. Posteriorly thei three pairs 
of grooves open into a common chamber, which in turn communicates 
with the exterior. 
The membranous labyrinth of smaller tadpoles (toes of foot already 
separately seen by naked eye as little knobs), I have carefully recon- 
structed from serial sections. The sacculus has the cochlea well 
developed and has the usual macula sacculi, m. lagenae and papilla 
acustica ; besides the papilla acustica the m. lagenae is further, more or 
less, separated into two maculae. The utriculus and the three semi- 
circular canals with the three cristae staticae, the macula acustica utriculi 
and the macula neglecta are also usual. The ductus endolymphaticus 
enters the cranium and swells into a large vesicle lying latero-dorsal to 
the brain, and containing an opaque limey fluid. 
In young tadpoles with the hind-limbs just beginning to show there 
n 
