140 
SIDNEY F. HARMER. 
epidermis. The junction between the muscular and non- 
muscular parts of the body-wall now lies at the distal end of 
the introvert, and the outermost layer in this region is the 
part of the non-muscular wall into which the more distal part 
has been invaginated. The invagination has resulted in the 
formation of a loop of the alimentary canal which passes 
distally along one side of the invagination. 
PI. 9, fig. 39, is in a similar condition, except that the 
introvert contains no tentacles. In their place may be seen 
a projection which obviously consists of a regenerating mus- 
cular part of the body-wall, terminated by a commencing 
lophophore. 
I am unable to give a satisfactory explanation of these 
appearances, although the fact that three or four specimens 
have been found in this condition shows that the complete 
invagination of the muscular body-wall happens not infre- 
quently. It is perhaps one of the methods by which the 
lophophore may be regenerated, as it seems probable, from a 
comparison of the two specimens figured, that PI. 9, fig. 41, is 
the earlier stage in the process, and that the invaginated ten- 
tacles would have been thrown off somewhat later, the wound 
closing, and the body-wall in that neighbourhood then growing 
out into the part seen inside the introvert in PI. 9, fig. 39. 
It is not obvious what the later course of the regeneration 
would have been, though it is possible that the introvert 
Avould have been evaginated and the muscular wall recon- 
stituted, partly from the old wall and partly from the portion 
which is being regenerated in PI. 9, fig. 39. It does not 
seem probable that the loss of the original lophophore always 
takes place in this way. It is not easy to explain the mechan- 
ism by which the complete invagination of the muscular part 
of the body-wall takes place in these cases. 
The condition shown in PI. 9, fig. 41, resembles that found 
in Ectoproct Polyzoa during the retraction of the tentacles, 
though the Phoronis has no retractor muscles comparable 
with those of the Polyzoa. The resemblance does not appear 
to me, however, to lend any support to the view maintained 
