70 
developed State, and, secondly, the animal was in excellent nutri- 
mental condition. The lumen, as well as the syncytical wall, 
abounds with yolk material. It must have been derived from rather 
I 
tremendous quantities of eggs. It is then rather easy to assume 
that these animals are not innocent guests of their hosts, but un- 
fortunately the digestive work is too far gone to allow safe conclu- 
sions as to the source of the eggs. It is of interest to mention that 
also the type specimen presented conditions in the alimentary sy¬ 
stem rather similar to the new ones. Beyond doubts one must take 
into account the extremely ferocious nature of the Polyclads when 
judging the State of things as to the nature of the livelihood of 
these animals in relation to their hosts. 
An extensive treatment of the nervous system will be spared 
for a later paper dealing generally with the conditions in Åcotylea. 
The brain belongs to the bi-lobed type (Text-fig. 19) and has an ex¬ 
tremely ventral position immediately above the muscular wall. It 
has already been stated (Bock 1913, p. 164) that the sensorial 
ganglions outside the capsula cerebralis (Lang’s „K6rnerhaufen“) 
are small. It may be added here that a substitute therefore exists 
inside the capsula in the antero-lateral part of the brain, on both 
sides, in the form of a greater collection of sensorial ganglion cells 
of the typical appearance, with small nuclei rich in chromatin cha- 
racteristic for the prae-cerebral ganglions. The large motorial 
ganglion cells of the brain extend on the sides, dorsally, ventrally, 
and laterally; the giant motorial cells are confined to the posterior 
half of the brain. Text-fig. 19 reproduces a drawing of the ventral 
nerves proceeding from the brain. They very soon anastomose 
richly with one another. The dorsal nerves have as usual a narrow 
calibre. The two large posterior ventral nerve trunks stand out 
perfectly even so far back as in the region of the genital apparatus, 
which they furnish with nerves (text-fig. 22). To give an idea about 
the rich anastomosing net-work of nerves I present two figures 
of the ventral nerve net (Plate II a, Fig. 6 and text-fig. 20). The 
more the periphery of the body is approached, the more the nerves 
subdivide and anastomose. Consequently the interspaces between 
the nerves are much smaller near the margin than farther away 
from it. Text-fig. 20 shows that this condition is gradually 
reached. A doser study of horizontal sections gives evidence that 
