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THE MICROSCOPE. 53 
‘The segmentation nucleus is central, and the cells resulting from the 
segmentation migrate slowly to the surface, the protoplasm forming a 
reticulum in the meshes of whichthe yolk is embraced. Some of these 
cells reach the surface to form the blastodern, while others remain 
behind to form “yolk cells.” On the third day the ventral plate and 
the rudiments of the amnion appear very early, the ventral plate 
becomes segmented, and paired appendages appear on every segment 
of the body. The primitive groove appears at the same time as the 
amnion, and develops from behind forward. It soon closes and 
forms a tube with a very narrow lumen behind, in front a solid cellu- 
larin-pushing. This is regarded as gastrulation, and the portion 
thus invaginated as ento-mesoderm, or primary entoderm, from 
the hinder portion of which cells are cut off, which wander in 
and join the “ yolk-cells,” but have nothing to do with the formation 
of the mesentoron. The remainder of the primary entoderm differ- 
entiates into two large lateral and a middle solid longitudinal band, 
and in each segment of the former there appears a cavity. The 
outer wall of this cavity forms the somatopleure, the inner the 
splanchnopleure and epithelium of the digestive tract. This inner 
wall soon separates completely from the outer in the middle line, 
and there becomes two-layered, thus developing both entoderm and ~ 
splanchnopleure. These lateral bands of entoderm now unite with 
the middle one and soon enclose the whole yolk and “the yolk-cells,” 
which latter degenerate and are absorbed. 
Hotorricuous Inrusoria Parasitic In THE ALIMENTARY CANAL 
or Wuite Ants.*—Mr. W. J. Simmons, induced by the discovery of © 
Prof. Leidy, of parasitic infusoria in the American white ant, has 
investigated the white ants of Calcutta, and presented his results 
before the microscopical society of that city. The alimentary canal 
of these ants, he says, teem in its lower portion with parasites. 
Although moniliform and ciliated and non-ciliated organisms, — 
bacteria, spirilla and nematoid worms were found, the present paper 
is devoted to the Holotricha Thisinfusorian is a free and rapid swim- 
mer. Owing to its constant changes in form, it varies in length and 
breadth—the measurements of four average individuals gave the fol- . 
lowing results: 
1. Length 73; “ Breadth zt; “ 
”? 5 
9. aan “i >) — a“ 
3 ” oF LEYS ee ” apo iy 
. 125 250 
4, 33 eeu > = “i 
*The Englishman, Calcutta, November 17, 1888.—Read before Microscopical Society 
of Calcutta. 
