174 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
with periblast-like conditions of the yolk-cells ; the enteron is then 
practically continuous with the segmentation cavity. General thinness 
of the down-growing blastoderm, whose Randwulst corresponds to the 
germ-ring ; close apposition of blastoderm to yolk-mass. Early appear- 
ance of embryo ; and, in general, early differentiation of the germ-layers 
of the blastopore’s dorsal lip, corresponding lack of differentiation of 
ventral lip. The mode of closure of the blastopore ; the presence of 
Kupffer’s vesicle, and the absence of neurenteric canal. Early growth of 
a solid neuron, early prominence of brain-mass, evanescent medullary 
groove, secondary acquisition of neural canal. The peristomial origin 
of the mesoblast ; its late differentiation ; the absence of gastric meso- 
blast. The early mode of establishment of the embryo’s outward form. 
Thus the embryological differences between Ganoids and Teleosteans 
are shown to be greatly lessened. 
Development of Teleostean Fins.* — Dr. R. G. Harrison has investi- 
gated the development of the paired and unpaired fins in the salmon. 
The pectoral fin arises as a thickening of the somatopleure. Muscle 
buds do not, as in other cases, enter into the composition of the rudi- 
ment. The protovertebrse of the pectoral region give off outgrowths 
from the ventral margin, which correspond not to muscle-buds, but to 
the ventral processes which give rise to the ventral musculature. The 
anterior outgrowths form the coraco-hyoid muscle, the posterior form 
the ventral muscles of the trunk. One of the latter, the fifth, reaches the 
base of the fin, and disappears, without, however, forming fin-muscula- 
ture. Muscle and skeletal parts arise from a single fin-rudiment. The 
following table is given : — 
Proto - 
vertebra 
Segment in 
Ventral Process 
Somatopleure. 
AT orrm 
in 
Adult. 
of Protovertebra. 
Embryo. 
a 
only mesen- 
absent 
p 
chyme 
thickening of 
1 
i. occipital 
mesenchyme 
> pericardial 
l region 
? 
2 
ii. occipital 
m. cor.-hyoid 
) 
hypoglossal > 
3 
i. trunk 
) 
1st spinal ■ 
l pectoral 
4 
ii. trunk 
> pectoral plate 
2nd spinal I 
r plexus 
5 
iii. trunk 
unites with next 
) 
3rd spinal J 
1 
6 
iv. trunk 
grows below fin 
as ventral mus- 
4th spinal \ 
secondary 
culature 
7 
v. trunk 
ventral muscu- 
no special 
5th spinal 
plexus 
lature 
? thickening 
8 
vi. trunk 
6th spinal \ 
trunk 
9 
vii. trunk 
1 
&c. ) 
' muscles 
Thymus Rudiments in the Lamprey.f — Herr J. Schaffer has dis- 
covered what he believes to be the thymus rudiments — hitherto unde- 
* Arch. f. Mikr. Anat., xlvi. (1895) pp. 500-78 (4 pis.), 
f SB. Akad. Wiss. Wien, 1894 (received Dec. 1895) ciii. pp. 149-56 (1 pi.). 
