464 EDGAR J. ALLEN. 
More doubtful points will be reserved for further investigation 
and a future communication. 
Embryos at various stages of development have been used, 
from the time when the eye-pigment first becomes visible 
until the time of hatching. An element which has once 
stained at any particular stage is found in practically the 
same condition at all later stages, excepting that the finer 
branches become more numerous, and, although the results 
as given all apply to late embryos, they have been obtained 
from embryos at different stages. For instance, in tracing 
certain fibres, which travel the whole length of the cord, 
although they can be readily recognised in late stages, they 
have only been actually traced throughout their entire length 
in much earlier ones. As a general rule, a fibre is most easy 
to trace through its whole length at the earliest stage at which 
it will stain. 
In the lobster embryo, as in the embryos of other Decapod 
Crustacea, the thoracic ganglia are fused together into one 
mass (figs. 1—4), which is united to the brain by a very short 
commissure (fig. 1, com.). At this stage the whole of the 
commissure which exists is the portion which in the adult lies 
between the commissural ganglia, from which the stomato- 
gastric nervous system arises, and the first thoracic ganglion, 
the stomatogastric commissural ganglia (fig. 1, st. com. gang.) 
being now immediately connected with the ganglia from which 
Antenne II are innervated (fig. 1, Ant. II), and forming part 
of the brain. The posterior portion of the brain of one side is 
connected with that of the opposite side by a transverse bridge 
(tr. br.), which lies immediately behind the cesophagus, and 
which in the adult lies behind the stomatogastric commissural 
ganglia. Eleven ganglia may be recognised in the fused mass 
in the thorax. Of these the first six go to form the anterior 
thoracic ganglion of the adult. In the present paper, for the 
sake of clearness, the ganglia will be distinguished as Th. I— 
XI. The ganglion cells of each of these eleven ganglia are 
arranged in four masses (blue in fig. 1), two lateral and two 
median, a median dorsal and a median ventral mass, one of the 
