IX. The Bryozoa 
ECTOPROCTA. 
About the earliest observations on the nervous system of 
these animals was by Dumortier and Van Beneden in 1848. They 
described the central nervous system of fresh water forms as com- 
posed of two ganglia above the oesophagus joined by commissures. 
From the aboral part of the ganglion a pair of nerves runs to the 
oesophagus. They also considered that a pair of nerves supplied 
the epistome. 
In 1848 Van Beneden speaks of but a single ganglion. 
Allman, 1856, in fresh water forms describes a single unpaired 
oval ganglion. The two oesophageal nerves are represented as an 
oesophageal ring with enervation for the epistome. 
Hyatt, 1865-1868, describes the central ganglion in Plumatella 
with the ganglion concentrated. The two long arms of the animal 
however, are capable of independent movement. The ganglion in 
Trederecella is spindle-shaped. In Plumatella the ganglion is kid- 
ney-shaped and as it doubles upon itself by movements of the 
animal it becomes heart-shaped. He describes a true nerve ring 
about the oesophagus. Nerves go to the middle and end intestine. 
Hyatt also describes nerves to the epistome and to the tentacles. 
Nitche, 1869-76, has studied bryozoans quite extensively. He 
found a central cavity in the ganglion in embryonic stages. He 
recognized an oesophageal ring, intestinal nerves, tentacle nerves. 
He recognized on the tentacles bristles which he called taste bristles. 
Claparede, 1871, in some bryozoans describes the nervous sys- 
tem of colonial forms; nerve strands running the length of the body 
were recognized. 
Kraepelin, 1887, found the center of the ganglion in adult 
forms, and the shape of the ganglion of fresh water forms elipsoid. 
He also recognized peripheral ganglion cells in the ganglion. Oral 
nerves were seen, as well as nerves to the epistome. 
Verworn, 1887, in a general way recognized ganglion cells. 
Saefftiger, 1888, has especially added to our knowledge of the 
distribution of the nerves to the tentacle crown; he also considers a 
sympathetic system but says nothing of the sense cells in the ten- 
tacles although he describes the epithelium of parts of the animal. 
Braem, 1890, describes the central ganglion of fresh water 
forms as hollow with an outer thinner oesophageal and a ventral 
thicker wall. He considers the inner part of the ganglion as largely 
fibrous. 
Oka, 1891, has considered fresh water forms, especially Pec- 
tinatella. Like Saefftiger, he finds the ganglion with a cavity in 
the mature state. The ganglion is compared to a spindle bent in 
