1046 The American Naturalist, [ December, 
some resemblance to the primitive streak of the Amniota, and 
to contribute as a growing point to the anterior end much as the prim- 
itive streak does to the posterior end of the embryo. 
Turning now to quite a different subject, the author affirms that i in 
all the vertebrate embryos he has examined there is a protoplasmic 
continuity between the different layers and organs. “The cells of the 
young embryo, subsequent to cleavage, are connected by delicate pro- 
cesses. There can be no reasonable doubt that it (the network of such 
processes) is derived from the processes and strands left between the 
cells as a result of the incomplete cleavage of the ovum.” Awaiting an 
investigation of this subject, which the author hopes to treat of in a 
future paper, he yet thinks “that there is, in my opinion, evidence to 
show that the whole of the nervous connections (by nerve-fibres and 
otherwise), both in the central organ and at the periphery, are devel- 
opments of this pre-existing network, which connects together at all 
times the whole of the cells derived from the fertilized ovum.” 
Embryology of a Nematode.—A welcome addition to the 
scant literature of this subject has been made by Benno Wandolleck* | 
He studied fresh and preserved material of Strongylus paradorus, a 
devising some new and interesting methods. a 
Peculiar changes in the arrangement of yolk-spherules precede — 
cleavage; the first plane is meridional and the cell at the animal pole, = 
where the polar bodies were formed, has no coarse yolk, while the cell 
at the other end of the elongated egg is completely full of it. The 
clear cell gives rise to all the ectoderm, and at first is where the anter- 
ior end of the animal will be; the granular cell gives rise to the ento- 
derm and the mesoderm, and is at first where the tail of the animal 
will be. The two cells rearrange themselves so that the ectoblast cell 
lies partly dorsal and the mes-entoblast cell partly ventral. 
Subsequent divisions result in a solid mass of cells in which the 
more numerous, smaller ectoblast elements form a dorsal cap over the 
few granular, larger mes-entoblast cells. As an epibolic 2 
begins to form, a pair of mes-entoblasts become recognizable as the 
mesoblasts, whence arise two simple rows of mesoblast cells, 
one on each side. These two longitudinal mesoblast rows run parallel 
with a aiam afte blewtenare slit formed by the overgrowing ecto- 
gi a blastopore closes completely the anterior part wags = 
point the mouth subsequently forms by a new invagination. The 
entoblast is now only two rows of few, large cells; ed 
“Archiv. f. Naturg, 58, 1892, pp. 123-147, plate IX. 
