1903. | ANATOMY OF A NEW GEPHYREAN WORM. 35 
thelium is furnished by a tentacular surface which is apparently 
external, 
sap seeming discrepancy is readily explained by a reference to 
the following diagrams (text-fig. 9), modified from Selenka, in 
which A represents the position of the mouth, B that of the 
cerebral ganglion, while thick-dotted lines indicate the relations 
of the tentacular wreath. 
Tn text-fig. 9 @ this wreath is seen surrounding the mouth with 
a simple circlet, as in Phascolosoma teres. In such a case the 
infundibuliform approach to the cerebral organ must be lined by 
cells, continuous not only with cells of the introvert epidermis 
but with those covering the outer aspect of the tentacular 
chaplet. 
Text-fig. 9, 
ger ae ad Ne. 
is XN io in \ ‘ 
/ a Fah eet uae 
| 5 \ ] ‘ 
1 A as ea 
\ | : ~. =? ; 
\ / A A 
& A ie of 
N Pa ee Bos ; 
ae Ebel a Senn ee Sees 
a b 
Tentacular wreath of (a) Phascolosoma and (6) Phymosoma. 
In text-fig. 95 the crown of tentacles is seen to have been in- 
dented in its upper (neural) part, and the edges of the indentation 
have been bent up in such a manner as to form a horseshoe- 
shaped lophophore which, partially encircling the brain, overhangs 
the mouth instead of surrounding it. The finely dotted line in the 
diagram represents the position of the “lower lip” in Phymosoma ; 
this may be looked upon as corresponding to the fused bases of 
aborted tentacles. Here, then, the brain, lying at the base of the 
lophophore, can only be approached by a canal whose walls are 
coated by an epithelium continuous with that covering the mesial 
surface of the tentacles. 
The arrangement seen in Phascolosoma is the more primitive. 
Briefly stated, tentacular surfaces which are inner and outer in 
the genus Phascolosoma, become outer and inner respectively in 
Phymosoma, owing to the secondary indentation of the crown of 
tentacles. 
According to Shipley (Joc. cit.), the space included within the 
concavity of the lophophore of Phymosoma becomes the repre- 
sentative of the ‘“ preeoral lobe ” of Phoronis. 
Qe 
34 
