520 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
This is the somewhat generalised form of the law which Mr. Galton 
sums up as follows : — “ Eachjparent contributes on an average one-quar- 
ter, or (0* * * § 5) 2 , each grandparent one-sixteenth, or (0*5) 4 , and so on; and 
generally the occupier of each ancestral place in the n th degree, whatever 
be the value of n, contributes (0*5) 2w of the heritage.” Prof. Pearson 
concludes his paper with the sentence, “ If Darwinian evolution be 
natural selection combined with heredity, then the single statement 
which embraces the whole field of heredity must prove almost as epoch- 
making to the biologist as the law of gravitation to the astronomer.” 
Formation of Breeds and Species.*— Herr H. Kohlwey has been 
led to some general conclusions as the result of many years’ experi- 
mental breeding of pigeons. In free-living forms especially, but also 
in domesticated breeds, external conditions are of great importance as 
evolutionary factors. He is convinced as to the inheritance of acquired 
characters, and finds in the environment a primary cause of variation. 
Even the colour of the birds is influenced, either indirectly through the 
nervous system, or directly. The offspring tend to resemble male parent 
or female parent, according to the relative potency of the germ-cells. In- 
breeding need not lead to degeneration if the stock be sound. Whether 
we accept the author’s main thesis or not, a contribution to evolution 
theory from a breeder is always of interest. We have not seen the 
original essay. 
b. Histolog-y. 
Centrosomes and Nucleus-t — Dr. B. Nemec compares cell-divisions 
in which the centrosome functions, with those in which the centrosome 
seems to be absent, as in higher plants. There is no doubt as to the 
essential resemblance ; and the author’s point is that in cells without a 
centrosome the nucleus serves the same purpose in the prophases and 
anaphases. In short, the centrosome is in such cells homodynamous 
with the nucleus before and after nuclear division. 
Structure of Cytoplasm.^: — Prof. J. Arnold has examined many dif- 
ferent kinds of cell with reference to the architecture of their substance. 
His method was to allow fragments of tissue to steep in potassium iodide 
iodine solution. In many cases, as in leucocytes and the cells of bone- 
marrow, plasmosomes are recognisable, bound by thread-like or rod-like 
processes into systems, sometimes reticular and sometimes spongy. The 
plasmosomes enclose granules (somatia) variously disposed, and there is 
a hyaline substance (paraplasm) in the interstices of the plasmosome 
systems. But with these materials great structural variety is possible, 
as the author shows. 
In a second paper, § dealing with nervous tissue, Arnold describes 
the general occurrence of rows of granules. In ganglion-cells there are, 
apart from the hyaline interstitial substance, at least two different sub- 
stances forming systems of granules. It may be that the one system, 
* ‘ Arten- und Kassenbildung. Eine Einfukrung in das Gebiet der Tierzuckt. 
Mit einem Vorwort von Dr. G. H. Th. Eimer,’ Leipzig, 8vo, 72 pp., 5 figs. See 
Biol. Centralbl., xviii. (1898) pp. 377-80; Zool. Centralbl., iv. (1897) pp. 569-70. 
t Anat. Anzeig., xiv. (1898) pp. 569-80 (18 figs.), 
t Arch. Mikr. Anat., lii. (1898) pp. 134-51 (1 pi.). 
§ Tom. cit., pp. 535-52 (1 pi.). 
