CILIATED PITS OF STENOSTOMA 245 
in eine hintere, durch eine breite Kommisur verbundene und 
eine kleinere, vordere Partie zerfallt. Die letztere bildet die 
beiden Griibschenganglien, in welche sich die Wimpergriibshen 
einsenken.? (Das Tierreich, s. 20.) According to our observa- 
tions, the ciliated pit-ganglion does not arise from the ‘brain’ 
but arises independently from the epidermis. 
In conclusion, it is interesting to observe the striking parallel- 
ism presented by this organ in its function and mode of origin 
with the olfactory organ of a vertebrate so far as its function 
(1.e., its function in the fish) and its mode of origin is concerned. 
This organ functions as a tester of the chemical nature of the 
water which passes through or over it as do the olfactory organs 
of the fish. Moreover, this organ arises as a modified region 
or plate in the epidermis. Some cells of this plate sink beneath 
the base of the plate to form the ganglion of the pit. All this is 
closely analagous to the following description of the origin of 
the olfactory ganglion as given by Minot (’92).8 
The ectodermal cells of the olfactory plate multiply, the kary- 
okinetic figures being found next to the outer or free surface of the 
layer; the cells thus produced assume the appearance of medullary 
neuroblasts and at four weeks are found migrating toward the mesen- 
chymal surface, so that the base of the layer of the olfactory ectoderm 
becomes crowded with nuclei; the protoplasm of these neuroblasts is 
collected on one side of the nucleus in a pointed mass; the cells now 
grow forth from the ectoderm and constitute the anlage ofthe ganglion 
between the ectoderm and the brain. (P. 637.) 
CONCLUSION 
The ciliated pit and its ganglion in this flatworm arise from 
the general epithelium in a manner closely analogous to the 
mode of origin of the olfactory epithelium and olfactory ganglion 
of the vertebrates. 
7 Italics our own. 
8 Minot; Human Embryology. 
