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SUMMARY OF CURRENT RESEARCHES RELATING TO 
Vascular System of Salmonid Embryos,* — Herr Ziegenhagen has 
carefully studied the successive phases of the circulation in Trout 
embryos, and describes the changes which take place in the vessels of the 
yolk-sac and the connecting trunks (sub-intestinal and hepatic veins). 
His results are based upon camera drawings of the living object at 
successive stages, upon injections of the vessels, and upon an extensive 
series of microphotographs of living embryos. 
External Views of the Developing Trout-egg.f — Herr Fr. Kopsch 
describes the successive external changes in the developing blastoderm 
of the Trout, from the morula to the tailed embryo stage possessing 
30-40 somites and three pairs of gill-slits. By means of a diagram 
he shows that the germinal disc grows backwards round the yolk, 
uniformly with the elongation of the embryo, until one-half of the yolk 
is covered. When the edge of the germinal disc, however, has passed 
the equator of the egg it grows more quickly below (i. e. away from the 
embryo) than in its upper part, and the rudiment of the embryo increases 
only slightly in length. 
A Zoophyletic Law of Development.^— Herr Tornier, as a result 
of his studies on the origin of the forms of joints, concludes that rnulti- 
and uni-functional joints have been derived phylogenetically from 
“universal” joints. He now points out that a similar law holds good 
for the evolution of the Vertebrate foot as a whole ; viz. that feet 
capable of only a minimal number of movements have been derived 
phylogenetically from feet capable of all kinds of movement. Not 
only is it true that the “ universal ” foot has preceded the multi- or 
uni - functional foot in phylogeny (cf. the evolution of the Perisso- 
dactyle limb), but it is also pointed out that “ universal ” Vertebrate-feet 
can be arranged in an ascending series according to the degree of differ- 
entiation exhibited by their joints. What is true of the individual foot 
is also true of the individual Vertebrate, considered as a machine for 
locomotion. There are land Vertebrates which can display all methods 
of locomotion, and others which can display only a definite number, 
or only one kind of locomotion. The forms possessing limited modes 
of locomotion have been derived from forms possessing every mode. 
This law the author would extend to the evolution of all other organisms 
and organ-systems. Animals adapted to a maximum of life-conditions 
are “ universal ” animals ; and these may be arranged in an ascending 
evolutionary series. At the base of this series stand those universal 
animals in the organization of which no division of labour has yet 
appeared, whose functions are not yet localized, and whose organs are 
not yet specialized ; and the higher stages of the series are furnished 
by animals showing increasing amounts of localization of function and 
specialization of organs. When an animal in the struggle for existence 
has become adapted to a reduced or minimal number of life-conditions, 
it has actually lost certain functions and certain organs, and must be 
ultimately derived from an ancestor of the “ universal ” type. Herr 
Tornier’s law may be summed up in the familiar statement that the 
specialized is derived from the generalized, and that the generalized 
* Anat. Anzeig., Erganzungsheft, ix. (1894) pp. 84-9. 
t Tom. cit., pp. 60-6 (1 fig.). % Tom. cit., pp. 102-8. 
