JUNE 26, 1902; 
NATURE 
2 
when a source of light was reflected from a metal surface 
covered with regular scratches or corrugations of a given form, 
but beyond this he does not remember having seen any other 
bookwork or examples on the same subject. A general investi- 
gation of the theory of brilliant points is now given by Mr. W. H. 
Roever in the Annals of Mathematics for April, pp. 113-128. 
When a ray of light emanating from a source which we will 
call P, is reflected at any surface, and an eye is placed at 
another point, P,, a point of the surface from which the reflected 
ray travels directly towards the eye appears luminous and is 
called by Mr. Roever a éril/iant point. A mathematical in- 
vestigation also involves the consideration of points from which 
the reflected ray travels directly away from the eye, and although 
such points obviously do not correspond to any visible pheno- 
mena, it is necessary to consider them under the name of virtual 
brilliant points. If the reflecting surface is a thin wire, a point 
P, will be a brilliant point if the lines P)P,; and P,P. make 
equal angles with the tangent line to the wire at Po. 
get the notion ofa brilliant point on a curve. Taking next a 
Fic. 
1.—Bright lines on a circular saw. 
finely but regularly scratched or corrugated surface, the locus 
scratches or corrugations is the brilliant curve of the system. For 
a doubly infinite series of curves, the equations of which contain 
two independent parameters, the mathematical theory leads to 
the consideration of a brilliant surface as the locus of the 
brilliant points, although it is not easy to see how this general- 
isation could be made the subject of experimental verification. 
The author, after giving a general investigation, considers the 
particular cases of the brilliant curve for a circular saw or disc 
of steel in which the scratches form concentric circles, and also 
for a rotating carriage wheel in which the curve is generated 
by the brilliant points of the spokes, z.e. of a family of radiating 
lines in one plane. In both cases the curves are of the fourth 
degree. The accompanying diagrams are reproductions of 
phctographs of some of the curves obtained with the circular 
saw. An obvious further example of loci of brilliant points is 
afforded when moonlight is reflected from waves or ripples on 
the sea or a lake. 
NO. 1704, VOL. 66] 
We thus | 
VARIA TION—GERMINAL AND 
ENVIRONMENTAL. 
es THE most critical and momentous period in the life-history 
of any plant or animal,” says Prof. Cossar Ewart, ‘‘is 
during the conjugation of the male and female germ-cells.” The 
variation which flows from this blending of the reproductive 
elements he speaks of as ‘‘ germinal.” That which occurs in 
the germ-cells up to the moment of conjugation, together with 
the variations during development and growth, he designates as 
‘* environmental.” 
It may perhaps be questioned in passing whether the dis- 
tinction is one that can always be observed in practice, and also 
whether Prof. Ewart’s terms are the best that could have been 
adopted. .However, they serve sufficiently well for the purpose 
of the paper before us. 
Some ‘‘congenital” characters, he proceeds, may be 
“acquired” ; for example, dwarfing due to embryonic malnutri- 
tion. The double uterus of a wild rabbit contained eight young 
in one division and four in the other, the weight of the two 
divisions with their contents being nearly equal. In such cases 
the offspring that has been starved before birth, should it survive, 
may eventually reach the normal size and produce normal de- 
scendants. Antenatal injury, as in constriction by the cord, may 
lead to ‘‘congenital” abnormalities which are neither ‘‘ inherited ” 
nor transmitted. 
Individual plasticity in response to environmental conditions 
is an obvious and undoubted fact. But can variations so induced 
be transmitted to descendants? This is still a burning question, 
in regard to which Prof. Ewart has as yet met with no evidence 
to support an affirmative answer. On the other hand, the results 
of his experiments have afforded much reason for the positive 
belief that the handing on in any form of acquired traits is 
extremely improbable. 
But although there is no evidence of the transmission of 
somatic characters acquired in virtue of individual plasticity, it 
is still possible that the general vigour of the somatic tissues 
may be reflected in the germ plasm, and also that the condition 
as to ripeness of the generative products may influence the nature 
of the combinations formed during conjugation. A young 
Jacobin-barb pigeon mated with an old turbit produced first two 
young ones which were devoid of all the distinctive points of 
both parents ; but afterwards, on several successive occasions, 
hatched out offspring which presented points of resemblance 
with the dam. Prof. Ewart declares that he can only account 
for this by saying that as the female parent increased in age and 
vigour her germ-cells increased in prepotency. When she went 
out of condition, the single offspring then produced more closely 
resembled the sire. 
Some experiments with rabbits led to unexpected results. 
Several white does were mated with wild males, and several 
wild does with a white buck. In every case the offspring 
resembled wild rabbits in form and colour. But the mating of 
the half-wild offspring with each other, uniform as they were, 
led to an ‘‘ epidemic of variation,”’ not only in colour, but also 
in size, disposition and other qualities. When the half-wild 
rabbits were crossed with white bucks or does, there were also 
always several colours represented in the cross-bred litters. An 
intimate relation was discoverable in all these and their offspring 
of the next generation between the colour, the “* wildness,” the 
time at which maturity was reached, and the rate of growth. 
| Though the half-wild progeny were all wonderfully like wild 
of the brilliant points with respect to the curves defined by the | 
rabbits, it was evident that in them the stability of the wild 
rabbit had been broken down. 
Further experiments with rabbits—one of which, narrated at 
length by Prof. Ewart, is of remarkable interest—tend to show 
that, as in the case of pigeons, the relative maturity of the male 
and female elements has a definite influence on the character of 
the offspring. The general results may be summarised as 
follows :—When insemination precedes ovulation, the young 
resemble the buck; when it follows, they resemble the doe ; 
when it coincides, some take after the buck, some after the doe, 
while others may differ from both parents and resemble some 
of the less remote ancestors. It was incidentally shown that 
in the rabbit, spermatozoa may retain their potency several 
days after they reach the fallopian tube. Prof. Ewart notes the 
1 ‘Variation: Germinal and Environmental.” 
F.R.S., Regius Professor of Natural History in the University o 
Edinburgh. Scientific Transactions of Royal Dublin Society, 19or 
p. 353-378. (Williams and Norgate). F 
By J. C. Ewart, M.D.» 
