The Morpliology of the Tadpole of Xenopus laevis. 257 
thymus (?) gland, along the outer, ventral surface of the eye to the skin ; 
(/3) to the skin behind the eye ; (y) to the skin above the brain and dorsal 
to the eye. 
5. The otic ganglion with several nerves to the membranous labyrinth 
is joined to the dorsal surface of the ventricle just behind the optic lobes. 
6. Small dorsal and ventral roots swell into a large ganglion just 
behind the auditory capsule. This ganglion gives off two nerves : 
{a) The glossopharyngeal, giving off (a) a branch which runs along the 
bar (PB2 Fig. 7) and goes to the pharyngeal grooves ; (/3) one running 
forwards dorsally to the thymus (?) gland and into the quadrate (Q Fig. 7) 
cartilage ; (y) one running ventrally to the thymus (?) gland and the quad- 
rate cartilage, along the dorsal surface of the pterygoid cartilage and into 
the muscles joining Meckel's cartilage to the palatine cartilage. 
[h) The vagus with branches to the oesophagus and lung. 
It will be noticed that although all ten nerves are developed they are 
joined to the brain by only six roots, which seems to indicate that the 
nerves are not outgrowths from the brain. This is, however, en j^assant, 
for only earlier stages than mine could decide such a question. 
Each spinal nerve also ends in an endo-vertebral ganglion, the small 
upward prolongation of which is closely applied to the latero-dorsal 
surface of the spinal cord, it being impossible to say definitely whether 
it is continuous with the cord or not, although I am of opinion that 
it is not. 
Except the vagus, I could find no nerves going to the splanchnopleure, 
so that the sympathetic cords must be developed late in the tadpole life 
(only two of my series were continued back far enough and stained 
suitably for the study of the spinal nerves). 
Eesume. 
1. The tentacular cartilages are joined both to the ethmoid and to 
the palatal portion of the sub-ocular arcade. 
2. The high epithelium of the gill-slits is continued into the glottis — 
in support of the theory that lungs and gill-slits are homologous. 
3. The operculum encloses three external gills which are fused 
distally to form three external gill-pouches. 
4. There are trabeculo-mandibular, mandibular-hyoid, and lst-2nd 
branchial thymus glands. 
5. In older tadpoles there are "lachrymal " (?) canals. 
6. The anteriorly situated articulation of Meckel's cartilage is 
discussed. 
7. There are two " pharyngo-branchials," one of which probably 
forms the stapedial portion of the columella auris. 
