EHBRYOLOGICAL. 
Gen, Sub. 49 
two chief results are (1) exogastrulation, and (2) an increase in the 
archenteric or endoderm-forming zone, which leads to a two-vesicled 
type of larva. Against the doctrine of specific areas, Herbst notes that 
the Pluteus outgrowths may arise from groups of cells which do not nor- 
mally form them. So is it with the ciliated bands when the calcareous 
needles are displaced. Therefore the author maintains the idioplasmatic 
equivalence of the cells in early stages ; Herbst (233). 
Artificial stimulus (clovo-oil, xylol, &o.), evoking production of vitelline 
membrane around unfertilized Echinoderm ova ; IIerbst (234). 
The position of the median plane of tho embryo is not determined by the 
position of tho first or second cleavage plauo. In various modifications 
of cleavage, produced by compression, &c., the nuclei are disposed in dis- 
orderly fashion, yet normal embryos result. Therefore there are no 
predetermined organ-forming areas or specialised substances definitely 
arranged. If one of the first two blastomeres be completely destroyed, 
the surviving half forms a fairly normal embryo. No semi-gastrula 
lateralis nor homi-embryo lateralis wore seen. The Mosaic theory of 
development is erroneous. So is the theory of germ-plasm. The ovum 
is a specifically organised “ elemeutarorganismus,” which develops epi- 
genetically, i.e., with gradual differentiation according to the mutual 
relations of the embryonic cells ; Hertwig (241, 242). 
Modification of segmentation of frog ova by gentle compression 
between two slides, or by confinement in glass tubes. The two poles of 
the nuclear spindle, defining the direction of the segmentation-plane, 
come to be in the direction of the largest protoplasmic parts. General 
conclusion : — that it is not cleavage which separates the ovum into quali- 
tatively specialised parts, the predisposition is in the unfertilised ovum ; 
Hertwig (242). 
Criticism of Hertwig. The first cleavages are qualitative partitions of 
the material which serves for the direct development of the four quarters 
of the embryo ; Roux (438). 
Influence of mercurial vapours on the embryo ; Dareste (121). 
Action of light and currents on development of Amphibians ; 
Camerano (87, 88). 
Effect of movement on the development of the eggs of the fowl ; 
Marcacci (337) : of light and various other influences ; Fer^ (156). 
Experiments on eggs of Ctenolabrus, Serraiius, Fundulus : Removal 
of blastomeres seems to show that the size of the embryo is determined 
by the amount of protoplasm present, and not by the quantity of nuclear 
material. The embryo cut off from all connection with the germ-ring 
on one side, elongates backwards, producing an embryo having both right 
and left sides alike and equal. The conclusion follows : In the elongation 
of the embryonic knob backwards the head remains a fixed point, and the 
elongation is due to an extension backwards of the mass ; the germ-ring 
takes no important part in the formation of the body of the fish 
embryo ; Morgan (363). 
Experiments on maturation and fertilisation in Ascaris niegalocephala : 
