. 
| Mar. 6, 1873] 
is produced a disc-like coagulation; their number rapidly 
increases, and this particular condensation becomes the embryo 
strictly so called, while the remaimder of the blastoderm 
serves only for its nourishment. The embryo soon begins 
to broaden into the form ofa biscuit. Three leaves or layers of 
cellules can be distinguished, superposed like envelopes upon 
each other, and each having its particular place in the construc- 
tion of the living being ; from the exterior leaf is formed the 
epidermis and the central parts of the nervous system, the spinal 
marrow and the brain ; from the central layer is formed the in- 
terior membrane which lines the digestive canal from the mouth 
to the anus, with all the glands that are attached to it (the lungs, 
the liver, the salivary glands, &c.) ; the intermediate layer is the 
source of all the other organs. 
The processes by which the three layers of cellules give birth 
to the most complicated organs can all be reduced—(1) To new 
segmentations, and consequently to an increase in the number of 
the cells ; (2) To the division of labour or the differentiation of 
these cellules ; (3) To the combination of these cellules, diffe- 
rently developed. The cellules which comprise a living orga- 
nism may thus be compared to the citizens of a state, some of 
whom have one set of functions to perform, others another ; 
the division of labour, and the organic perfection which results 
from it, enables the state to accomplish certain undertakings 
which would be impossible to isolated individuals, Every living 
organism composed of many cellules resembles a sort of republic 
capable of accomplishing certain organic functions, which could 
not be discharged by a single cell, an ameéa, or a monocellular 
plant. No rational mind would seek to explain by superhuman 
intervention the public weal which accrues to political society, 
from the harmony of particular actions ; so also in the organism, 
all the adaptations to ends ought to be regarded as the natural 
_ and necessary consequence of co-operation, of the differentiation 
_ and the perfection of the cellules, and not as the intentional work 
of a supernatural will. 
Until the brain begins to show itself distinctly, it is scarcely 
possible to recognise any difference between the embryos of the 
different vertebrata, or at least of the three superior classes— 
reptiles, birds, and mammals. Why, then, should any one now 
refuse to admit the most important consequence of the theory of 
evolution, according to which men have descended from simious 
or even inferior mammals? Are the phenomena of the develop- 
ment of the individual man, the earliest characteristics of which 
are given above, less marvellous? Is it not in the highest degree 
astonishing that all the vertebrate animals, belonging to the most 
diverse classes—fishes, amphibia, reptiles, birds, and mammals 
-—cannot, in the earliest stages of their embryonic development, 
be distinguished from each other, and that even at a much later 
stage, when reptiles and birds are distinctly separated from 
mammalia, man and the dog are still almost identical? The 
development of the individual (ov¢ogevests) is as difficult to ex- 
plain as that of the species (Phy/ogenesis). It may be even said 
_ that it is still more so, seeing that it has an infinitely shorter time 
_ in which to be accomplished. The former is nothing more than 
a compact reproduction of the latter, and Haeckel rightly finds 
in this parallelism the most incontestible proof in favour of the 
theory of evolution. Man and the superior vertebrata reproduce 
in the earlier phases of their development conditions which last 
through the life of the lower orders of fishes ; they then pass into 
_ forms which are characteristic of the amphibia ; the marks of the 
mammalia appear only at a later stage, and even here are dis- 
covered a succession of degrees which correspond to the charac- 
ters of different species or families. It is the same order in 
which the palzontological history of the earth shows us the suc- 
cessive production of the different animal forms—first the fishes, 
then the amphibia, next the inferior mammals, and last the 
superior mammals. 
Side by side with these two orders of evolution there is a 
third parallel with them: it is that which is found particu- 
larly expounded in the works of Cuvier, Goethe, Meckel, 
Johannes Miiller, Gegenbaur, Huxley, and forms the subject of 
comparative anatomy. This science seeks to determine what is 
common to the forms of different species, and studiés living 
beings from the point of view of the scale of perfection. In 
this respect also we find that fishes, amphibia, and the inferior 
mammals stand in the same relation to man as from the stand- 
point of embryonic evolution and of palzontology. Now, this 
triple parallelism of individual development, of palzeontological 
development, and of systematic development, is completely 
explained by the theory of transformation, by the laws of 
NATURE 
353 
heredity and adaptation, while no opponent of the theory of 
evolution has ever been able to account for it in a natural and 
philosophic manner. Haeckel concludes from this that we 
shall be compelled to admit Lamarck’s theory of evolution, if we 
are not led to accept Darwin’s theory of selection. 
SOCIETIES AND ACADEMIES 
LonDON 
Royal Society, Feb. 20.—‘‘On the Anatomy of the Land 
Planarians of Ceylon.” By H.N. Moseley, M.A., Exeter Col- 
lege, Oxford. : 
Two new species of Land Planarians from Ceylon are described 
as belonging to the genus Jifadivm (Stimpson), 2. Ceres, the 
other to that of Ryzchodemus, R. Thwaitesit. 
With regard to the habits of Bipalium, the most interesting 
facts noted are that these animals use a thread of their body- 
slime for suspension in air, as aquatic Planarians were ob- 
served to do for their suspension in water by Sir J. Dalyell, and 
the cellar-slug does for its suspension in air. The anatomy of 
the Planarians was studied by means of vertical and longitudinal 
sections from hardened specimens. The skin in Bifalium and 
Rynchodemus closely conforms to the Planarian type, but is more 
perfectly differentiated histologically than in aquatic species, and 
approaches that of the leech in the distribution, colour, and 
structure of its pigment, and especially in the arrangement of the 
glandular system. The superficial and deep glandular systems of 
the leech are both here represented. In 2. Ceres peculiar glan- 
dular structures exist, which may foreshadow the segmental 
organs of Annelids, it being remembered that these segmental 
organs are solid in an early stage of development. Rod-like 
bodies are present in abundance, though, singularly enough, Max 
Schultze failed to find any in Geof/ana. These rod-like bodies 
are probably homologous with the nail-like bodies of Nemer- 
tines ; and it is possible that the setze of Annelids are modifica- 
tions of them. 
The muscular arrangement in 2ipalium, which is very complex, 
throws great light on the homologies between the muscular layers 
of Zurbellaria and those of other Vermes. In Sifalium there 
isan external circular muscular coat, which even presents the 
same imbricated structure which is found in it in leeches and other 
worms. In Dendrocalum lacteum there is also an external circu- 
lar coat. In cases where a distinct external circular muscular 
coatis absent, it is represented by a thick membrane, which is 
very probably contractile. All Turbellarians are built on the 
same essential type, as regards muscular arrangement, as are 
other worms. ‘The general muscular arrangements in the bodies 
of the Bifalium and Rynchodemus haye become much modified 
from those of flat Planarians by the pinching together and con- 
densation of the body, but they are nevertheless referable to the 
same type. 
The digestive tract consists of three tubes, one anterior, two 
posterior, as in other Planarians, and as in the embryo leech 
before the formation of the anus. Characteristic of land Plana- 
rians, and consequent on the condensation of the body, is the 
absence of all diverticulze from the inner aspects of the two pos- 
terior digestive tubes. The close approximation of the intestinal 
diverticula in Bipalium and Rhynchodemus, and the reduction 
of the intervening tissue to a mere membranous septum, is very 
striking, and seems to foreshadow the condition of things in 
Annelids. The great difference in the form of the mouth in 
Rhynchodemus and Bipalium is also remarkable, considering the 
many points in which these forms are closely allied. 
A pair of large water-vascular trunks, or, as they are here 
termed, primitive vascular trunks, are conspicuous objects in 
transverse sections of the bodies of Bipaliam and Rhynchodemus. 
A peculiar network of connective tissue is characteristic of these 
vascular canals on section, and is shown to present exactly 
similar features in Leftoplana tremellaris, Dendrocelum lacteum, 
and Bothriocephalus latus. The close agreement in the relative 
position of the oviducts to the vascular canals in Dendrocalum 
and our land Planarians is very remarkable. The nerves and 
ganglia of Planarians lie within the primitive vascular system, as 
do the corresponding structures within the primitive body-cayity 
of the leech. ; 
A small marine Planarian was found to contain hemoglobin. 
In Aifalium there are a series of separate testes disposed in 
pairs, asin the leech. In Rhynchodemus the testicular cavities, 
