GEPHYREA 161 
Phymosoma varians is a West Indian species found em- 
bedded in the soft coral rock, in which it bores tubular 
passages, probably dissolving the soft rock by some chemical 
excretion. Its colour is brownish-yellow. In its extended 
condition it is about 5 cm. long and about $ em. broad, 
tapering at each end. ‘The anterior half of the body, the 
introvert, can be withdrawn into the posterior half, just as 
the finger of a glove can be invaginated into the hand. 
The mouth is terminal, and is at the end of the introvert. 
Dorsal to the mouth is a crown of eighteen or twenty short 
tentacles arranged in a horse-shoe, the lophophore (Figs. 103 and 
105). The dorsal ends of this horse-shoe are continuous with 
the dorsal ends of a thickened lower lip, between which and 
the crown of tentacles or lophophore the mouth opens. The 
mouth has therefore the form of a crescentiform slit. In 
the hollow of the horseshoe-shaped lophophore the skin is 
wrinkled and pigmented; close beneath it, and in direct con- 
tinuity with it, les the bilobed supra-oesophageal ganglion. 
About 2 mm. behind the mouth, a very extensile fold of tissue 
forms a ring-like collar round the base of the head. ‘This 
collar can be produced so as to cover in the whole head. 
The introvert is distinguished from the rest of the body 
by the presence of numerous rows of minute chitinoid hooks 
(Fig. 103), which alternate irregularly with certain papillae 
to be described below. 
The integument consists of the following layers: (i.) the 
ectoderm, (i1.) circular muscles, (i1.) longitudinal muscles, and 
(iv.) peritoneal epithelium. The ectoderm is a single layer of 
cubical cells. Those covering the lower lip, and that side of 
the tentacles turned towards the mouth, bear cilia. The 
ectoderm of the concave side of the lophophore and its hollow 
is crowded with black pigment, and at two places it is con- 
tinuous with the substance of the brain. Over the rest of the 
body the ectoderm secretes a thick cuticle, which is only 
broken by the presence of the skin papillae. 
These papillae are very characteristic of the Gephyrea ; 
they are formed by the ectoderm becoming folded into the 
shape of a double narrow-mouthed conical cup. The outer 
layer of cells resembles the ordinary ectoderm ; the inner, how- 
abil 
