ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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studded with scattered goblet or mucus-secreting cells. The yolk-sac 
is also remarkable for the presence of a layer of smooth muscular fibres 
under the epidermis, which appears to originate from the splanchnic 
mesoblast. Nothing of this kind seems to be known in the yolk-sac 
of any other young fish. There is no reason for supposing, as some 
ichthyologists have, that the fixation of the young is a voluntary action. 
The Origin of Blood from the Endoderm.* — Herr H. K. Corning 
describes peculiar strands of cells in the endoderm of embryos of 
Tropidonntus natrix at the gastrula-stage, and inclines to think that 
they are connected with the endodermic formation of blood. The same 
appearances were seen in the gastrula-stage of Lacerta agilis, but with 
less distinctness. Herr Corning notices that Kupffer, in 1882, described 
similar strands in the gastrula-stage of Coluber JEsculapii, and inter- 
preted them as vascular structures, but traced them to a “ parablastic ” 
origin, or, in other words, to the much-discussed yolk-nuclei. 
£. Histology. 
Streaming Movements of Protoplasm.-)- — Prof. C. Frommann main- 
tains that the movements of fluids in what may be called the “ artificial 
cells ” made by Quincke and by Biitschli are in many ways different 
from those exhibited by living matter. Quincke sought to explain 
streaming movements by supposing a periodic distribution of albuminoid 
soap along the surface of the plasma, but this would not explain the 
occasional coexistence of streams in opposite directions within the cells 
of Tradescantia or Urtica, nor the occasional sudden stoppage or even 
reversal of movement, nor several other characteristics of protoplasmic 
movement. As to the relations between protoplasmic streaming and 
that of fine foam globules, e. g. those of Biitschli’s emulsions, &c , it 
must be remembered that the former is retarded and stopped by cutting 
off the supply of oxygen, which is sufficient evidence of the dependence 
of the movement on metabolism. In regard to Blitschli’s theory of the 
predominantly vacuolar structure of protoplasm, Frommann admits what 
he has previously demonstrated in detail, that there are many illustra- 
tions of vacuolated protoplasm, that in many cases the structure is rather 
that of a broken than of a complete network, that framework and network 
may result from the modification of vacuoles with originally intact walls, 
but he urges, as he may naturally do with some confidence, that in many 
cases apart from the presence of vacuoles there is a genuine network. 
Cell-Structure.f — Dr. K. C. Schneider finds that both the protoplasm 
and the nucleus of cells have a homogeneous framework, the bars of 
which are directly connected through the nuclear membrane. This 
framework consists typically of looped fibres of equal thickness, which 
have the power of uniting with one another and so giving rise to mem- 
branes. This formation of membranes may be very well seen in cells 
rich in vacuoles, such as the eggs of Ascaris megalocephala. When the 
vacuolation is very considerable almost all the free fibres may pass into 
* Arch. f. Mikr. Anat., xxxvi. (1890) pp. 516-27 (1 pi.), 
f Anat. Anzeig., v. (1890) pp. 648-52, 661-72 (4 figs.), 
j Zool. Anzeig., xiv. (1891) pp. 44-6, 49-50. 
