564 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
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 collateral branches to the 
neuropile in each ganglion through which it passes ; these may either 
decussate with the corresponding element of the other side, or pass down 
on the same side of the cord as that on which the cell lies. (B) Each 
element consists of a fibre starting from a cell in one of the thoracic 
ganglia, and running forward to the brain. (C) Each consists of a 
small cell in the anterior portion of the lateral mass of ganglion cells ; 
the fibre, after taking a Z-shaped course through the neuropile, to which 
it gives off numerous arborescent branches, turns backwards, and, after 
running between a fibre of series D and the central mass of ganglion 
cells, ends in a tuft of fine branches at the posterior end of the ganglion 
next behind that in which the cell is situated. (D) These elements are, 
as already indicated, associated with series C, and both groups generally 
stain in the same preparation ; their cells lie in the posterior portion of 
the lateral ganglionic mass ; the fibre of each element passes forwards, 
giving off numerous arborescent branches to the neuropile ; it enters the 
ganglion next in front, and ends in a terminal tuft which lies exactly 
opposite the terminal tuft of one of the C elements, and behind a lateral 
tuft which is formed by the D element of the next ganglion ; the three 
tufts lie at exactly the same level in the cord, and are all in the focus 
of the Microscope at the same time. 
Development of Gebia littoralis.* — Mr. P. Butschinsky reports that 
the ova of Gebia have a large quantity of nutrient yolk ; the first cleavage 
is in the interior of the yolk, and the eight cleavage-nuclei that are 
subsequently formed make their way to the surface of the egg. The 
nutrient yolk partly becomes united with the unsegmented central yolk- 
mass, and partly becomes completely separated from it. The final result 
is a blastula formed of a superficial layer of cells, and an internal 
vitelline mass. At this period some of the cells wander into the yolk, 
and form a small number of vitellophages. These degenerate and soon 
disappear almost completely. 
A blastodermic thickening appears on the ventral side of the egg, 
and in it three separate swellings can be distinguished ; the germinal 
layers begin to be formed very early ; the mesodermal laj^er, at its first 
appearance, has a paired structure, and consists of cells which are 
arranged in two longitudinal rows. The nervous system commences in 
the Nauplius-stage, and when the creature begins to lead a free life 
eighteen ganglionic swellings can be seen. The mesodermal cells do 
not form regular somites, but are scattered quite irregularly ; they give 
rise to the heart and gonads as well as to the muscles. The dorsal 
surface of the heart remains open for a certain time, and the opening is 
covered by ectoderm. The gonads arise in the latest stages of embryonic 
life and are paired ; some of the mesodermal cells increase rapidly in size 
and form the beginnings of the genital cells. The mid-gut is developed 
from two endodermal “ Anlage ” which are primitively separate ; the 
hinder of these is closely related to the proctodseal invagination, and 
has the edges of its cup-shaped mass directed forwards. At the same 
time a similar collection of cells appears near ther stomodaeum, and has 
* Zool. Anzeig., xvii. (1894) pp. 253-6. 
