LIFE-HISTORY OF BUCEPHALUS HAIMEANUS. 661 
and are smaller than the parenchyma nuclei, as the rudiment 
of the penis sheath, and a rounded mass of slightly larger 
nuclei, as the rudiment of the testes (figs. 1 and 41). 
THe Nervous System. 
Immediately behind the cystogenous organ lies the brain, 
consisting of halves united by a broad commissure. ‘he 
brain consists of a fibrous mass in which lie a few scattered 
ganglion-cells (figs. 35, 36, 43). 
The cells or nuclei which Ziegler has described as ganglion- 
cells I believe to be simply parenchyma nuclei which serve as 
a sort of incomplete sheath for the nervous system (figs. 43, 
n.s.; 35 and 36, par.n.). My observations on this point con- 
firm those of Schwarz (35) on Cercaria armata, C. 
echinata, etc. 
From the brain are given off anteriorly four comparatively 
large nerves, composed of many fibrils. The nerves rapidly 
subdivide, the branches being distributed to the anterior end 
of the body. The cystogenous organ is especially richly sup- 
plied. Posteriorly, two main trunks are given off from the 
brain (fig. 43). These pass backward along the ventral side 
of the body, giving off branches to the pharynx and continu- 
ing to the tail region. Scattered ganglion-cells may be seen 
throughout the course of these nerve-trunks. 
The rudiment of the brain appears in the embryo soon after 
the beginning of elongation from the germ-ball stage (fig. 13). 
At first it is simply a nearly solid aggregation of nuclei 
apparently no different than the usual parenchyma nuclei. 
From this mass of tissue fibrous elements and ganglion-cells 
are gradually developed. 
The use of methylene blue as an intra-vitam stain confirmed 
observations which I had previously made on ganglion-cells 
in material stained with iron hematoxylin. Time has not 
permitted the use of other and more modern methods. 
vot. 49, PART 4,—-NEW SERIES, 48 
