138 
SIDNEY F. HARMER. 
each of these regenerated a complete individual, is too 
precise to be disputed. But in P. oval is I have found no 
certain evidence that the muscular region shares the power 
of division which is undoubtedly possessed by the non- 
muscular region. It is possible that PL 8, fig. 10, indicates 
that fission may occur in the muscular region, since in this 
case the longitudinal muscles are well differentiated in a frag- 
ment which is only just beginning to develop a new lopho- 
phore. PL 9, fig. 35, may also imply that the fission-zone 
was formed just distally to the junction of the two regions of 
the body-wall. But in most of the specimens drawn, the mus- 
cular part is at first indicated merely hy a thickening of the 
body-wall, and no distinct muscle-fibres can be recognised 
in the early stages. The regeneration of the distal end in 
fact commences, as has already been pointed out, with the 
regeneration of a muscular region, and the lophophore ap- 
pears subsequently at the distal end of the muscular region. 
The general result of these observations is that fission may 
occurin P. ovalis at practically any point of the non-muscular 
body-wall, and that very small fragments separated off in 
this way are capable of complete regeneration. No certain 
evidence has been obtained that the muscular part can form 
fission-zones, though this possibility is not excluded. A lobed 
condition of the proximal end of the body, as shown in Pl. 9, 
figs. 32, 36, 39, appears to indicate that the ampullar region has 
not been completely reconstituted since the last fission took place. 
Many of the individuals, whether regenerating or not, show 
a great development of the adipose tissue which accompanies 
the two longitudinal blood-vessels. In many cases, as in Pl. 7, 
fig. 6, PL 9, fig. 29, the body-cavity of a regenerating fragment 
contains a large quantity of this tissue, which may probably 
be regarded as a reserve of nutrient material, at the expense 
of which the fragment can continue to survive until it has 
reconstituted its alimentary canal and has formed a new 
orifice to its tube. Larger specimens which have developed 
a considerable amount of this tissue are probably in a favour- 
able condition for undertaking fission ; and it may be noticed 
