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desk os Hise a Aa ee 3 a 
1892.] Embryology. 1043 
cal plane (whence the eight cells, four above and four below, result). 
Now by the application of pressure it is possible to force all these 
spindles to lie in one plane, whence there results a plate or single layer 
of eight cells. These cells may remain in this abnormal position and 
divide vertically so that there are two layers of eight or in all sixteen 
cells, which subsequently divide tangentially. A little consideration 
will convince one that here cells, or nuclei, normally forming part of 
only one pole, give rise to parts of both poles. Since these confused 
cleavage cells may proceed to form normal plutei their indifferent, 
omnipotent character cannot be disputed. 
These and other experiments, not here revealed, lead Hans Driesch 
to the following conceptions of the value of cleavage: (1) Cleavage 
forms a homogenous, indifferent material any portion of which, almost, 
may form a complete organism when isolated or any part of an organ- 
ism when united with other portions. (2) The embryo acquires form 
through unknown laws of correlation ; it is not a mosaic as Roux has 
maintained. 
Budding in Hydroids.‘—Contrary to the usually received con- 
ception, Mr, Albert Lang, working with Prof. Weismann, contends 
that in hydroids buds are formed not by equal outgrowth of both 
ectoderm and entoderm, but primarily by the growth of the ectoderm 
alone, this germ layer early giving rise to a new entoderm for the bud. 
In an introductory note Prof. Weismann relates that purely the- 
oretical reasons, the probability that “bud idioplasm” is confined to 
certain cells of the ectoderm, led him to doubt the participation of the 
entoderm in the formation of hydroid buds. 
The body of the paper is devoted to a description of sections made 
through very early stages in the budding of Eudendrium racemosum, 
E. ramosum, Plumularia echinulata, and Hydra grisea, preserved for- 
_ the most part with the aid of corrosive sublimate. 
Although in the stages usually examined the ectoderm and entoderm 
of the bud are continuous with those layers in the adult and surround 
8 prolongation of the gastric cavity of the adult, yet the study of very 
early stages shows that this continuity does not arise by mere prolifer- 
ation in each layer. At first there is a thickening of the ectoderm 
Over the area that is to give rise to the bud; here the basement mem- 
brane appears to be dissolved; is at all events absent; thus ectoderm 
and entoderm are here continuous with one another; rapid cell divis- 
ton takes place in the ectoderm, while the entoderm seems to remain 
“Zeit. f. Wiss. Zool., 54, July, 1892, pp. 365-383. 
