HAMAKER: NERVOUS SYSTEM OF NEREIS VIRENS. 91 
results by fixing in a 1% to 5% solution of acetic acid saturated with 
corrosive sublimate. Preparations fixed in this way were stained on the 
slide with Heidenhain’s iron-hematoxylin. The osmic acid method of 
vom Rath (95) gives results in many ways equally good, and for some 
purposes, such as tracing nerves, even better than the corrosive and 
iron-hæmatoxylin method. I found a mixture in the following propor- 
tions of osmic acid, picric acid, acetic acid, and platinic chloride very 
satisfactory : — 
Omicidi 270. MEA AAC, LA ec 
Piorio acid, sat. aq. sol. , , , 100% 
Pinto hlorida 24. wo A 200% 
AO LIO AI. se A, 166 
The results obtained are not at all uniform in quality, since the rate of 
preeipitation of the osmium by the pyroligneous acid seems to vary. 
The value of successful preparations, however, counterbalances the 
capriciousness of the method. The results obtained by these two 
methods agree in almost every particular, even to the relative intensity 
of the stains in the various tissues. 
For intra-vitam staining the following method proved most success- 
ful. Specimens of Nereis having about seventy segments were injected 
with a concentrated solution of methylen blue in normal salt solution. 
They were then laid, ventral side uppermost, in a moist chamber for 
about two hours, after which the stain began to appear in the sub- 
esophageal ganglion, From this region the stain gradually penetrated 
eaudad, and when it was thought to have reached its optimum, it was 
fixed by Bethe’s (95) ammonium molybdate method. The objects were 
then embedded in paraffine and cut. 
PART I. DESCRIPTION. 
1. TOPOGRAPHY. 
The central nervous system of Nereis virens is well developed. 
Throughout the entire length of the body the ventral nerve cord ex- 
hibits a sharp differentiation of ganglia and longitudinal connectives. 
The ganglia are segmentally arranged and constant in position; the 
nerves are regularly arranged in metameric groups of five pairs each 
(Plate 1, Fig. 8). The ventral cord lies deeper than the hypodermis, 
from which it is partially separated by the circular muscle bundles. 
