524 
could desire. There are with them Mastodons which simplify 
our knowledge of this group ; and among the last discovered 
remains Sirenians, which, in presenting a certain similarity to 
the afore-named Meeritherium, strengthen the belief in the 
proboscidian relationships of these aquatic forms. Finally, and 
perhaps most noticeable of all, there is the genus Arsinoitherium, 
a heavy brute with an olfactory vacuity which outrivals that of 
Grypotherium itself, and is surmounted by a monstrous fronto- 
nasal horn, swollen and bifid, for which the most formidable 
among the Titanotheres might yearn in vain. There is an 
occiput to match! The suggestion that this extraordinary 
beast has relationships with the Rhinoceridz is absurd, since its 
tooth pattern alone inverts the order of this type. That it is a 
proboscidian may be nearer the mark, and if so it shows once 
more how subtle were the mammals of the past. Great as is 
this result, much remains to be done or done again, if only from 
the fact that in seeking to determine homologies our American 
brethren, in the opinion of some of us, have placed too much 
reliance ona so-called tritubercular theory of tooth genesis, of 
which we cannot admit the proof. How, we would ask, is it 
conceivable that a transversely ridged molar of Diprotodon type 
can be of tritubercular origin ? 
Sufficient for the moment of palzeontological advance, except 
to remark that the zoologist who neglects this branch of 
morphology misses the one leavening influence ; neglects the 
court on whose ruling arguments deduced from embryological 
data alone must either stand or fall. We may form our own 
conclusions from facts of the order before us; but it is when we 
find their influence on the master-mind prompting to action, like 
that of Huxley with his mighty memoir of 1880, in which he 
revised our subclass terms, that we appreciate them to the full. 
With this consideration we pass to the living forms, and I 
have only time in dealing with these to comment on advance 
which affects our broadest conceptions and classifications of the 
ast. 
r To commence with the Mammalia, we now know that the 
mammary gland when first it appears is in all forms tubular, 
and that this type is no longer distinctive of the Monotremata 
alone. We know, too, that the intranarial position of the 
epiglottis when at rest, long known for certain forms, is a 
distinction of the class. It explains the presence of the velum 
palatinum, by its association with the glottis for the restriction 
of the respiratory passage, the connection being lost in man 
alone, under specialisation of the organ of the voice. 
Similarly, the doubly ossified condition of the coracoid may 
now be held diagnostic, for it is known that the epicoracoidal 
element, originally thought to characterise the monotremes 
alone, is always present, and that reduction to a varying degree 
characterises the metacoracoid, which retires, as in man, as the 
so-called coracoid epiphysis. 
Our conceptions of the interrelationships of the Marsupialia 
and Placentalia have during the period we are considering been 
delimited beyond expectation, by the discovery of an allantoic 
placenta in a polyprotodont marsupial, in place of the vitelline, 
present in its allies. When it is remembered that in the forma- 
tion of the placenta of the rabbit and a bat there is realised a 
provisional vitelline stage, it is tempting to suggest that thé 
evidence for the direct relationship of the two mammalian sub- 
classes first named overlaps (there being a placental marsupial 
on the one hand, a marsupial placental on the other), much as we 
have come to regard Archeopteryx as an avian reptile, the 
Odontornithes as reptilian birds. These facts, moreover, 
prove that the type of placenta inherited by the Placentalia 
must have been discoidal, and that from that all others were 
derived. 
Equally important concerning our knowledge of the 
Marsupialia is the discovery, first made clear by Prof. Syming- 
ton, of this College, that Owen was correct in denying them a 
corpus callosum. How Owen arrived at this conclusion it is 
difficult to conceive; but in these later days the history of 
discovery is largely that of method ; and it is by the employ- 
ment of chrome-silver, methylene-blue, and other reagents, which 
in differentiating the fibre-tracts enable us to delimit their 
course, that this conclusion has been proved. By the corpus 
callosum we now understand a series of neo- pallial fibres which 
transect the alveus and are present only in the Placentalia. 
There is no department of mammalogy in which recent work 
has been more luminous than this which concerns the brain ; 
and, to mention but one result, it may be said that in the 
renewed study of the commissures there has been found a fibre- 
NO. 1717, VOL. 66] 
NATURE 
[SEPTEMBER 25, 1902 
tract characteristic of the Diprotodontia alone, so situated as to 
prove that they and the Placentalia must have specialised on 
diverse lines from a polyprotodont stock. Interesting this, the 
more, since the phalangers and kangaroos are known to be 
polyprotodont when young. And when we add the discovery 
that in the detailed relationship of its commissures the brain of 
the Elephant Shrew, a lowly insectivore, alone among that of 
all Placentalia known, realises the marsupial state, as does its 
accessory organ of smell, we have to admit the discovery of 
annectant conditions just where they should occur. 
The morphological method is sound ! 
The master hand which has given us this result has also 
reinvestigated the Lemurs. From an exhaustive study of the 
Lrain or its cast of all species of the order, living and extinct, 
there has come the proof that the distinctive characters of the 
lemuroid brain are intelligible only on a knowledge of the 
pithecoid type; that its structural simplicity in the so-called 
lower lemurs is due to retrogressive change, in some species 
proved to be ontogenetic ; and that the Tarsier, recently claimed 
to be an insectivore, is a lemur of lemurs. It is impossible to 
over-estimate the importance of this conclusion, which receives 
confirmation in recent paleontological work; and there is 
demanded a reinvestigation of those early described Tertiary 
fossil forms placed on the Ungulo-lemuroid border line, as also 
a reconsideration of current views on the evolution of the 
primates and of man. 
In dismissing the Mammalia, we recall the capture during the 
period we review of three new genera, a fourth, the so-called 
Neomylodon, having proved by its skull to be Gryfotherium 
Darwinit, already known. The African Okapi, an object of 
sensation beyonds its deserts, has found its place at last. To 
have been dubbed a donkey, a zebra and a primitive hornless 
giraffe is distinction indeed ; and we cannot refrain from con- 
trasting the nonsensical statement that its discovery is ‘ the 
most important since Archeopteryx ” with the truth that it is a 
giraffine, horned for both sexes, annectant between two groups 
well known. As a discovery it does not compare with that of 
the Mole-marsupial, and it falls into insignificance beside that 
of the South American diprotodont Ccenolestes, the survivor of 
a family which there flourished in Middle ‘Tertiary times. 
Passing to Birds and Reptiles, it will be convenient to 
consider them together. A knowledge of their anatomy has 
extended on all hands, and in respect to nothing more instruc- 
tively than their organs of respiration. Surprise must be 
expressed at the discovery, in the chelonian, of a mode of 
advancing complication of the lung suggestive of that of birds. 
On looking into this, I find that Huxley, who rationalised our 
knowledge of the avian lung and its sacs, was aware 
of the fact that in our common Water-tortoise (Ayzys 
orbicular?s), the lung is sharply differentiated along the bronchial 
line into a postero-dorsal more cellular mass, an antero-ventral — 
more saccular, of which the posterior vesicle, in its extension 
and bronchial relationships, strangely simulates the so called 
abdominal sac of birds, He had already instituted comparison 
with the Crocodiles, aud was clearly coming to the conclusion 
that the arrangement in the bird is but the result of extreme 
specialisation of a type common to all Sauropsida with a ‘‘cellu- 
lar” lung. The respiratory process in the bird may be defined 
as transpulmonary, and it is an interesting coincidence that, as 
I write, there comes to hand a memoir, supporting Huxley’s 
conclusion, and establishing the fact that there is a fundamental 
principle underlying the development and primary differentiation 
of all types of vertebrate lung. 4 
The discovery of the Odontornithes in the American Creta- 
ceous is so well known, that it is but necessary to remark that 
nine genera and some twenty species are recognised. To 
Archeopteryx I shall return. Before dismissing the Chelonia, 
however, it must be pointed out that paleontology has définitety' 
clenched their supposed relationship to the Plesiosaurs. Of all 
recent paleontological collections there are none which, for care 
in collecting and skill in mounting, surpass the reptilian remains 
from the English Jurassic (Oxford Clay) now public in our 
national museum. The Plesiosaurs of this series must be seen 
to be appreciated, and nothing short of a merciful Providence 
can have interposed, to ensure the generic name Cryptocleidus, 
which one of them has received, since the hiding of the clavicle, 
its diagnostic character, is an accomplishé€ fact. It is due to 
secondary displacement, under the approximation in the middle 
line of a pair of proscapular lobes, present in the Plesiosauria 
and Chelonia alone, and until the advent of this discovery mis- 
