STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 27o 
ticulum from the vestibule, at a later stage pinched off as a sac 
containing a small lumen (Taf. xxx, fig. 40, g). It appears to 
me, however, unlikely that Hatschek’s account is perfectly cor- 
rect. Fig. 12 is a horizontal section through a Pedicellina. 
The ganglion ( ga .) is oval, and consists of a peripheral layer 
of cells, enclosing a central fibrous mass, as in Loxosoma. 
In order to transform Hatschek’s ganglion rudiment into the 
adult condition it would be necessary to atrophy the lumen 
and to replace it by a development of nerve-fibres. The latter 
would thus be formed from the primitively external surface of 
the cells, a conclusion which appears most improbable, since 
the position in which nerve-fibres originated phylogenetically 
was no doubt the deeper surface of cells which formed part of 
the outer ectoderm. This consideration, as well as the history 
of the ganglion in Loxosoma, leads me to suspect that the 
lumen in Hatschek’s ganglion is in reality the commencement 
of the fibrous tissue, which in optical sections might easily be 
supposed an empty space. Similarly Nitsche (10) has described 
the ganglion of Alcyonella as originating as a diverticulum 
from the tentacle sheath. I regard it as probable that the 
explanation which I have suggested for Pedicellina will hold 
also for A lcyonella. 
Salensky has pointed out the similarity between the two 
posterior sense organs of L. crassicauda and the similar 
organs of Rotifera (vide Mobins, No. 9, Taf. v, fig. 2). These 
organs in Brachionus consist of a pair of bunches of fine 
hairs, borne laterally on the surface of the body, and each 
supplied by a nerve from the brain. Mobius describes, further, 
certain bipolar ganglion-cells passing by means of a nerve- 
fibril directly to the body-wall, although no tactile hairs are 
described in this position. 
Alimentary Canal. — The general characters of this system 
are already well known, and a reference to the figures accom- 
panying this paper will sufficiently explain its anatomy. 
Behind the mouth (fig. 11) is a large epistome, the size of 
which has hitherto been hardly sufficiently recognised, and in 
extent, indeed, is not far inferior to the buccal shield of 
