286 
ther distribution of the fibres. This experiment shows that the fibres 
from the most anterior cells must extend for seven, or more, spinal 
segments before ending in, or leaving the cord. 
The neurites rarely pass to the right and left fibre bundles altern- 
ately. Asa rule they will enter one of these bundles from two, three, 
or four consecutive cells. But, on the whole, they are evenly divided 
between the bundles, as my notes on the asymmetry, or rather the 
symmetry of the nervous system of this fish will testify. The neu- 
rites enter the bundles from their mesal surfaces and when from 25 
to 35 fibres have thus entered, they are partitioned off by a septum 
of neuroglia. These septa are vertical, so that further caudad in the 
cord the bundle appears to be made of several separate parts. 
No embryonic material of Paralichthys dentatus was obtainable. 
Pleuronectes americanus. 
The giant cell apparatus is most specialized in this genus. There 
are only about 75 cells in all in the adult, and these are of large 
size. The first is placed just behind the union of the restiform bodies 
as in the Paralichthys. But the others are much further apart, 
usually about four to ten times their own diameter, and the last cell 
is found between the 10th and 14th spinal segments. 
The cells lie slightly deeper in the cord than in Paralichthys 
and their grouping into threes and fours is not so noticeable because 
of the greater distances which separate them. The numerical distri- 
bution of the cells is shown by the following table: 
Ist to 4th segment 29 cells 
bth’ he oth) oe 2253 
TOth she Gbhe uss Oe he 
And now about the cells themselves. They very greatly in size, 
the larger ones being about 0,19 or 0,20 mm in diameter, and the 
smaller ones about 0,10 mm in diameter. This variation in size is 
very noticeable because there are very few cells of intermediate sizes. 
The large ones are found in the posterior portion of the apparatus, 
as well as in its anterior part. 
The structure of the cell is very different from that of the same 
cell found in Paralichthys. The chromophyllic substance is arranged 
in larger masses in the cytoplasm and these masses are long and 
spindle-shaped. 80 per cent of the cells possess 2 or 3 nuclei 
(see Fig. 2) and I have counted 6 and 7 nuclei in one or two Cases. 
From the dumbbell figures that I have seen assumed by the nucleus 
and all the stages between this and two distinct nuclei, I believe that 
