STUDIES ON THE NERVOUS SYSTEM OF ORUSTACEA. 465 
latter only being shown in the figure. The spaces between the 
ganglion cells (left white in fig. 1) are occupied by masses 
of nerve-fibre, the “ punkt-substance” of Leydig, or to adopt 
the more appropriate name suggested by His,' the neuro- 
pile. 
When, shortly after the hatching of the larva, the thoracic 
ganglia separate, the median masses of ganglion cells of the 
embryo divide transversely, the anterior portion going to one 
ganglion, the posterior to the ganglion immediately behind it. 
In fig. 1 the dotted line between Th. VI and Th. VII represents 
the line of this division. 
In the abdomen the six ganglia are separate in the embryo, 
as in the adult. 
In the following description a ganglion cell, together with 
the fibre springing from it, will be termed a nerve element. 
These elements may be divided into three main groups: 
I. Elements which lie entirely in the ganglionic chain, and 
which must be supposed to serve the purpose of co-ordinating 
the action of its various parts. 
II. Elements which consist of a ganglion cell in the cord, 
and a fibre which runs out at a lateral nerve-root. Some at 
least of these elements, possibly all, are connected with muscles, 
and are motor elements. 
III. Sensory elements, consisting of cells outside the 
central ganglionic chain and fibres running from them to a 
ganglion. 
I. Co-orpinatinc Exements. (Figs. 2—4.) 
These elements may be divided into four classes: 
A. Elements (fig. 2) made up of a cell in the brain or one of 
the ganglia, and a fibre which runs posteriorly to the end of 
the cord, giving off in most cases collateral branches to the 
neuropile in each ganglion through which it passes. 
B. Elements (fig. 3) made up of a cell in one of the ganglia 
1 His, ‘‘ Histogenese und Zusammenhang der Nervenelemente,” ‘ Archiv 
Anat, u. Entwickelungsgesch. Anat. Abt.,’? Supp. Bd., 1890. 
