1016 General Notes. [October, 
muscular wall of the heart, and which underlies the fore-gut as a 
transverse band of tissue. The cardiac lumen, as observed by 
myself to appear in the living embryo, occupies, ad initio, such a 
position that the median vertical plane passing through the em- 
bryo lengthwise would divide it. 
Its floor, which corresponds to its future venous end, seems to 
be devoid of cells, and is formed apparently by the periblast cov- 
ering the yolk. In the later stages of cardiac development in 
forms which have no complete circulation at the time of hatching, 
this is invariably the case, the venous end of the heart opening 
directly upon the surface of the periblast, as is shown in longi- 
tudinal sections of such stages. 
As elsewhere stated, the yolk is here absolutely excluded from 
the intestine, and the arrangement above described then provides 
the passage-way for yolk material into the general circulation as 
it is segmented off from the periblast, as shown by Kupffer, 
Gensch and myself. This also bring the segmentation cavity and 
the blood vascular channels into actual continuity. 
The investigations of Hoffmann! upon the development of the 
heart in Salmo are based entirely on sections, and begin with a 
stage long prior to the time when the organ begins to pulsate, 
and corresponds pretty closely to the stage of development seen 
in the cod embryo described above, which was observed about 
two days before pulsation began, when the heart became for the 
first time distinctly tubular, its lumen in the early stage here con- 
sidered, being a mere flat, discoidal vacuole with vertical side- 
walls formed of cells. At a later stage of development the axis 
of the lumen of the cardiac cavity is horizontal instead of 
vertical. 
Hoffman concludes that the endothelium of the heart is derived 
from the hypoblast, in which a short tubular cavity at once ap- 
pears, the long axis of this endothelial tube coinciding in direc- 
tion with the axis of the embryo. The myocardium or muscular 
outer wall of the heart is derived from the splanchnopleural 
_ plates which grow on either side of the embryo from above down- 
wards and inward under the fore-gut, below which they approxi- 
mate, their free ends finally investing the endothelial vesicle or 
tube, which represents in the salmon the vacuole above described 
in the cod embryo, which is the first trace of the cardiac lumen. 
After the muscular layer of the heart is supplied by the splanch- 
nopleural plates, the foundation of the structure of the adult 
_ heart has been laid. : 
= — In neither of the foregoing accounts is there anything which 
_ Suggests very much similarity between the mode of development 
_ of the first traces of the unpaired rudiment of the teleostean 
heart and that of Aves or Mammalia which arises by the fusion 
the median line of a pair of cavities on either side of the lat- 
enie der Knochenfische, Pts. vir, viii. Amsterdam, 1882. 
