ON PHORONIS OVALIS, STRETB1LL WRIGHT. 
127 
proximal end of an individual ; and it seems necessary to 
assume that the faculty of producing a tube and of boring 
in the shell is possessed by a considerable part of the body- 
wall. 
Structure of the Animal. 
Owing to its small size many of the principal points in the 
structure of this species can be made out in stained prepara- 
tions of the entire animal mounted in Canada balsam. The 
frequent occurrence of regenerating lophophores gives rise 
to an extraordinary want of uniformity in the appearance of 
the individuals. The even more striking variation in size, as 
exemplied, for instance, by PI. 7, figs. 2 and 5, appears to 
be due to the reduction in length produced by transverse 
fission. 
A. specimen with expanded lophophore is represented in 
PI. 7, fig. 1. The small number of the tentacles is at once 
apparent, and it constitutes one of the most characteristic 
features of the species. How striking is the difference 
between P. oval is and some other species of the genus 
may be illustrated by the comparison with P. buskii, the 
number of whose tentacles is estimated by de Selys-Long- 
champs (1907, p. 33) at about one thousand. 
In the great majority of the specimens the tentacles lie in 
their retracted condition inside the tube. This condition of 
the tentacles is shown in PL 7, fig. 3, and other figures. In 
favourably prepared specimens (PL 9, fig. 40) the epistome 
(ep.) can be seen as a distinct lip overhanging the mouth and 
surrounded by the bundle of tentacles. 
The distal part of the body-wall is thick (PL 7, fig. 3), a 
condition which is largely due to the presence of strong 
bundles of longitudinal muscles. These end abruptly at 
about the middle of the length of the body in this particular 
individual, although the proportion which the muscular part 
of the body-wall bears to the non-muscular part is highly 
variable. In PL 7, fig. 2, for instance, the muscular region 
