Bauhaus-Universität Weimar

NATURE 
492 
[April 5, 1877 
The tail is likewise curved up underneath, and lies with 
its broad surface towards the body, turning either towards 
the right or the left, and thickening part of the hinder 
extremities. In three examples the extremities are fully 
developed, and even show the characteristic discs on the 
tops of the toes. In the fourth example all four extremi¬ 
ties present short stumps, and as yet show no traces of 
toes, whereas, as is well known, in the Batrachia anura 
generally the hinder extremities and the ends of the feet 
first appear. Neither of branchiae nor of branchial slits 
is there any trace. On the other hand, in the last-men¬ 
tioned example, the tail is remarkably larger, and has its 
broad surface closely adherent to the inner wall of the 
vesicle, and very full of vessels, so that there can be no 
doubt of its function as a breathing organ. As develop¬ 
ment progresses, the yelk-bag on the belly and the tail 
become gradually smaller, so that at last, when the little 
animal, being about 5 mill, long, bursts through the enve¬ 
lope, the tail is only 1*8 mill, in length, and after a few 
hours only 03 mill, long, and in the course of the same 
day becomes entirely, absorbed. Examples of the same 
batch of ova, which were placed in spirit eight days after 
their birth, have a length of from 7 0 to fS mill., whence 
we may conclude that their growth is not quicker than in 
other species of Batrachians. 
The development of this frog, Dr. Peters observes (and 
probably o{ all the nearly allied species), without metamor1 
phosi-q v ithout branchiæ, with contemporaneous evolution 
of the anterior and posterior extremities, as in the case of 
the higher vertebrates, and within a vesicle, like the amnion 
of these latter, if not strictly equivalent to it, is truly re¬ 
markable. • But this kind of development is hot quite 
unparalleled in the Batrachians, for it has long been known 
that the young of Pipa amencana come forth from the 
eggs laid in the cells on their mother’s back tailless and 
perfectly developed. In them, likewise, no one has yet 
detected branchiæ, and we also know from the observa¬ 
tions of Camper,1 that the embryos at an earlier period are 
provided with a tail-like appendage, which in this case 
also, may be perhaps regarded as an organ of breathing, 
possibly corresponding to the yelk-placenta of the hag- 
fish. As regards this point, also, Laurenti says of the 
Pipa : “ Pulli ex loculamentis dorsi prodeuntes, metamor- 
phosi nulla?” (Syn. Rept., p. 25.) 
It would he of the highest interest, Dr. Peters adds, to 
f ollow exactly this remarkable development on the spot. 
The development of the embryo of these Batrachians in a 
way very like that of the scaled Reptilia makes one suspect 
that an examination of the temporary embryonic structures 
of Hylodes and Pipa would result in showing remarkable 
differences from those of other Batrachians. The general 
conclusions which might be drawn from this discovery are 
so obvious, says Dr. Peters, in conclusion, that it would be 
superfluous to put them forward. 
A subsequent communication of Dr. Peters to the 
Academy informs us that it had escaped his notice that 
M. Bavay, of Guadaloupe, had already published some 
observations on the development of Hylodes martini- 
censis.* According to his observations, on each side of 
the heart there is a branchia consisting of one simple 
gill-arch, which on the seventh day is no longer discern- 
iole. On the ninth day there is no longer a trace of a 
tail, and on the tenth day the little animal emerges from 
the egg. M. Bavay also observed the contemporaneous 
development of the four extremities, and hints at the 
function of the tail as an organ of breathing. 
The observations of Dr. Gundlach, therefore, says Dr. 
Peters, differ in some respects from those of M. Bavay. 
It would be specially desirable, however, to ascertain 
whether tire arched vessel on each side of the heart is 
really to be regarded as a gill-arch, or only as the in¬ 
cipient bend of the aorta. 
1 Comm. Soc. Reg. Golfing. Cl. phys. ix p. 135 (178$). 
Ann, £c. Nat. ser. 5, xvii., art. No. 16(1873.} 
TYPICAL LAWS OF HEREDITY1 
\1TE are far too apt to regard common events as 
* * matters of course, and to accept many things as 
obvious truths which are not obvious truths at all, but 
present problems of much interest. The problem to 
which I am about to direct attention is one of these. 
Why is it when we compare two groups of persons 
selected at random from the same race, but belonging to 
different generations of it, we find them to be closely 
alike ? Such statistical differences as there may be, are 
always to be ascribed to differences in the general con¬ 
ditions of their lives ; with these I am not concerned at 
present, but so far as regards the processes of heredity 
alone, the resemblance of consecutive generations is a 
fact common to all forms of life. 
In each generation there will be tall and short indi¬ 
viduals, heavy and light, strong and weak, dark and pale, 
yet the proportions of the innumerable grades in which 
these several characteristics occur tends to be constant. 
The records of geological history afford striking evidences 
of this. Fossil remains of plants and animals may be dug 
out of strata at such different Jevels that thousands of 
generations must have intervened between the periods in 
which they lived, yet in large samples of such fossils we 
seek in vain for peculiarities which will distinguish one 
generation taken as a whole from another, the different 
sizes, marks and variations of every kind, occurring with 
equal frequency in both. The processes of heredity are 
found to be so wonderfully balanced and their equi¬ 
librium to be so stable, that they concur in maintaining 
'a perfect statistical resemblance so long as the external 
conditions remain unaltered. 
If there be any who are inclined to say there is no 
wonder in the matter, because each individual tends to 
leave his like behind him, and therefore each generation 
must resemble the one preceding, I can assure them that 
they utterly misunderstand the case. Individuals do not 
equally tend to leave their like behind them, as will be 
seen best from an extreme illustration. 
Let us then, consider the family history of widely dif¬ 
ferent groups ; say of ioo men, the most gigantic of their . 
race and time, and the same number of medium men. 
Giants marry much more rarely than medium men, and 
when they do marry they have but few children. It is a 
matter of history that the more remarkable giants have 
left no issue at all. Consequently the offspring of the ioo 
giants would be much fewer in number than those of the 
medium men. Again these few would, on the average, 
be of lower stature than their fathers for two reasons. 
First, their breed is almost sure to be diluted by 
marriage. Secondly, the progeny of all exceptional 
individuals tends to “revert” towards mediocrity. Con¬ 
sequently the children of the giant group would not 
only be very few but they would also be compa¬ 
ratively short. Even of these the taller ones would be 
the least likely to live, It is by no means the tallest men 
who best survive hardships, their circulation is apt to 
be languid and their constitution consumptive. 
It is obvious from this that the ioo giants will not 
leave behind them their quota in the next generation. 
The 100 medium men, on the other hand, being more 
fertile, breeding more truly to their like, being better fitted 
to survive hardships, &c., will leave more than their pro¬ 
portionate share of progeny. This being so, it might be 
expected that there would be fewer giants and more 
medium-sized men in the second generation than in the 
first. Yet, as a matter of fact, the giants and medium¬ 
sized men will, in the second generation, be found in the 
same proportions as before. The question, then, is 
this :—How is it that although each individual does not 
as a rule leave his like behind him, yet succèssivegenera- 
tions resemble each other with great exactitude in all 
their general features ? 
1 I^pture delivered at the Royal Institution, Friday evening, February 
9, by Francis Gallon, F R.S.
        

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