ON PENNELLA BALZINOPTERZA. 415 
papilla-like tubercles formed the most marked feature of the summit. Hach had 
a definite chitinous envelope, which inclosed an areolated tissue, the areole of 
which varied materially in size, and corresponded in character with the tissue in 
the axis of the arms to be subsequently described. 
Within the tuberculated summit numerous transversely striped muscular fibres occu- 
pied a large proportion of the space dorsally and laterally closed by the chitinous 
envelope. They arose from the inner surface of the envelope, which in transverse sec- 
tion had a ridge and furrow-like character. The muscular fibres in this region situated 
laterally to the mesial plane converged from their origin and seemed to end in 
a common tendon, which was attached to the papilla-like tubercles situated on the 
side of the cleft which formed the oral aperture (figs. 5, 7, 8). Their apparent 
function was to draw the sides of the cleft asunder, widen the aperture, and by 
successive contractions and relaxations to convert the cleft into a suctorial mouth. 
In transverse sections of the head below the tubercles the muscular fibres were 
less numerous; those situated in proximity to the mesial plane converged on the 
dorsal wall of the alimentary canal, on which they could act directly as dilators. 
The fibres situated further from the mesial plane reached the dorsal aspect of a 
pair of bodies, to be immediately described, which stained readily with carmine. 
The striped muscular fibres were seen as low down as the origin of the arms, 
but they were absent immediately below these appendages, and their place was to 
a large extent taken by the areolated tissue. 
I have more than once referred to a tissue, which I have named ‘ areolated,’ situated 
in the head, in the part of the body immediately below the head, and in the arms 
into which it was prolonged at their base of attachment. In a subsequent section I 
shall have to call attention to a similar tissue in the abdomen. Koren and 
DantEtssEeN described a layer of adipose matter, in most places not very thick, 
though it could form isolated fatty agglomerations; in the head, arms and the upper 
thoracic division of the body it formed a thick stuffing, and corresponded in its 
position to the areolated tissue seen in my specimens: the adipose tissue was composed 
of fat cells, which, they say, had one or more ramifications on the cell. 
In its general characters the areolated tissue consisted of a meshwork of connective 
tissue, continuous with the membranous lining of the chitinous wall of the parasite. 
In the strands of this meshwork, more especially in its peripheral part, nucleated 
cells were seen in places in considerable numbers, which in size and general 
appearance were not unlike leucocytes. The areole of the meshwork varied in 
size, the largest being just visible to the naked eye, whilst the smallest required 
a magnification of two hundred to three hundred diameters. In specimens taken 
from the head, when the tissue was teased with needles and examined in glycerine, 
| the areolze were seen to contain rounded or ovoid cells, which, like fat cells, refracted 
the light strongly, and showed the characteristic reaction of fat with osmic acid ; 
in the act of teasing, many of the fat cells were ruptured and oil globules escaped. In 
