166 
PROFESSOR A. M. PATERSON ON THE DEVELOPMENT OF 
blue-black. They were in the same condition of development as the Mouse embryos. 
The spinal nerves (aS^.M., Plate 22, fig. 4) w^ere distinctly fibrous, terminating in a 
thickened brush-like ending in the neighbourhood of the cardinal or jugular vein (P.). 
The dorsal ganglia [D.G.) were well defined, and consisted of fusiform cells with large 
ovoid nuclei, and with long and fine processes directed towards the spinal cord and 
nerve. In transverse sections a more or less rounded mass of cells {Sy.) is seen lying 
between the aorta or carotid artery, and the cardinal or jugular vein (P.). It is 
formed of a mass of cells closely packed together and sharply marked off from the 
ordinary mesoblast by a capsule composed of a single layer of flattened cells, which, 
like the blastema-cells in which the mass is imbedded, stain less deeply than the mass 
itself The cells forming this group, besides being evident from their deeper staining, 
possess nuclei, which have a striking appearance in transverse sections. Some are 
large and prominent, with several nucleoli; others are very small ; while some cells 
appear to be without nuclei. In transverse sections they are round or angular. 
These appearances are due to the fact that the cells are fusiform, and so are cut at 
different levels in transverse sections. The mass, as a whole, is in close proximity to 
the aorta or carotid artery. It is distinct and separate from the spinal nerves. It is 
traceable in transverse sections from a point slightly anterior to the root of the fore¬ 
limb to the middle of the trunk, being thickest in front, and gradually becoming- 
attenuated and indistinct behind. 
In longitudinal (sagittal) sections of embryos from the same uterus, prepared in the 
same way, one can make out by means of continuous series of sections that this 
apparently rounded mass is distinctly evident on either side of the middle line as a 
long rod or column of fusiform cells {Sy., Plate 26, fig. 11), possessing large, deeply 
stained, ovoid nuclei, and fine thread-like processes. vVll the cells are directed antero- 
jDosteriorly, and bear a inarked resemblance to the cells of the dorsal ganglia at this 
date {D.G.). The column lies in close proximity to the aorta and carotid vessels 
{Art.), and can be traced forwards as far as the level of the mouth {Mo.) and first 
vertebral segment {Ist V.S.), where it ends abrujDtly in a pointed brush-like process 
composed of the filiform processes of the cells, and not apparently due to any admix¬ 
ture of fibres. It is marked off from the surrounding tissues by a narrow but distinctly 
evident interval. Behind the level of the lungs the column of cells becomes less 
distinct; it can, however, be followed to the anterior end of the kidneys (Wolffian 
bodies), where it becomes connected with a mass of mesodermal cells, whuch form one 
portion of the suprarenal bodies. Above and behind the kidneys the character of the 
column changes. It can be followed to the level of the hind limbs, but is more 
indefinite; its cells, while retaining their fusiform character and columnar arrange¬ 
ment, are less closely packed together, are less regularly arranged, and are less deeply 
stained than in the anterior part of the column. Traced backwards, it becomes more 
and more indistinct, and is finally lost in the region of the hind limbs. In its entii e 
length I failed to find any connexion between this cellular column and the spinal 
