OX PHOKON1S OVA MS, ST RETHILL WRIGHT. 
139 
that the specimen shown in process of dividing in PL 9, 
fig. 29, is well provided with adipose tissue. The regenera- 
tion of the lophopliore without fission may also be facilitated 
by the previous deposition of a sufficient reserve which can 
be drawn on for the nourishment of the other tissues during 
the temporary closure of the alimentary canal. It may be 
noted that the intestine of a regenerating fragment without 
a functional lophopliore frequently contains the remains of 
Diatoms, which must have been taken in during a period 
when well-developed tentacles occurred. 
The presence of a large amount of adipose tissue is not, 
however, a necessary prelude to fission, even though it may 
favour this process. Some of the specimens of full length 
are remarkable for being of smaller diameter than usual, 
their tissues being more transparent than in other cases, and 
the adipose tissue being deficient in amount. These seem to 
be ill-nourished individuals, and their occurrence probably 
accounts for certain abnormally slender regenerating frag- 
ments, of the kind shown in PI. 9, fig. 38, which are some- 
times found. The muscular part of the body-wall has com- 
menced to differentiate in PI. 9, fig. 38, and although it& 
small diameter points to a want of vigour, this individual, and 
others like it, may have been in a condition to complete tlio 
regeneration. 
The Occasional Complete Invagination of the Muscular 
Part of the Body-Wall. 
In several cases individuals have been found in the peculiar 
condition shown in PI. 9, figs. 41 and 39. In PI. 9, tig. 41, 
the partial invagination which normally occurs at the proximal 
end of the muscular body-wall has become so complete a& 
to result in the invagination of the whole of the lopho- 
phore and of the tentacles. The invaginated muscular wall 
is now turned entirely inside out, forming a sheath 
opening distally (or.), containing the tentacles ( tent .), and 
having its epidermal portion lining the cavity of the intro- 
vert and its longitudinal muscles on the outer side of the 
