640 
the echidna. 
tile egg is very large, and tliat consequently there is only a partial segmentum (meroblastic 
typ®)- The egg is laid at an age equal to a thirty-hour-old chick, and is enclosed in a strong, 
flexible, white shell. The latter is three-quarters of an inch long, and half an inch broad’ 
The Ornithorhynchus lays two at a time ; the Echidna one. The former places the eggs at the 
end of one of its burrows ; the latter in a ventral pouch.” 
It seems, then, that these two mammals actually do lay eggs. The latter are hatched, in 
one case by the warmth of the stomach-pouch in which it is carried, and in the other it is 
dependent on the warmth of the sun or the nursing of the mother. 
Speaking in the anniversary meeting of the Royal Society, in November, 1883, Professor 
Huxley said : u It certainly is high time that British science should deal with a problem of 
the piofoundest zoological interest, the materials for the solution of which abound in and are 
at the same time confined to those territories of the Greater Britain which lie on the other side 
of the globe.” These words had reference to the series of investigations which Mr. Caldwell— 
the first Balfour student— had then gone to Australia to prosecute with regard to the embry- 
ology of the lowest mammalian forms — the monotremes and marsupials. 
Somewhat less than a year later, August, 1884, and whilst the British Association was 
holding its meetings in Montreal, Professor Mosely, the President of the Biological Section, 
was enabled to communicate the following brief but suggestive message from Australia: 
“Caldwell finds monotremes oviparous, ovum meroblastic.” Brief as was the message, it yet, 
as Professor Mosely said, contained the most scientific news which had been communicated to 
the Association in Canada. 
Zoologists will now look forward to the publication of Mr. Caldwell’s more detailed 
account of his investigations. That monotremes are oviparous has been maintained by various 
naturalists for now some sixty years, but up till the present time no sufficient evidence has 
been brought forward to place the matter beyond dispute, the chief difficulty in elucidating 
the problem lying in the fact that the two curious groups of animals which alone are placed 
in the monotremata inhabit exclusively the Australian region, and hence have been studied 
but little in their native habitat. 
Though the two are closely allied, yet the Ornithorhynchus and Echidna differ markedly 
from each other in external appearance — the one being adapted to the water, having its feet 
webbed, and its muzzle of that peculiar shape which has earned its present title of Duck-bill 
Platypus ; while the other is essentially a land animal, feeding on ants, which it licks up by 
means of a long, flexible tongue, and having its body covered with sharp spines, much as a 
hedgehog. 
The question how these animals reared their young, and in what condition the latter were 
born, has long been a matter of much dispute, and for information we are indebted to Horne, 
Mechel, Groff, St. Hilaire, and perhaps most of all to Owen. 
In 1829, St. Hilaire laid a communication before the Royal Academy of Science in Paris, 
in which he stated his opinion that the monotremes could no longer be admitted among the 
mammals, nor could they be classed with birds or reptiles, but they must, though including 
only two groups of animals, be formed into a distinct fifth class among vertebrates, the order 
being as follows : Mammals, Monotremes, Birds, Reptiles, and Fishes. An interesting part of 
his paper is the following: “A Mr. Holmes, while shooting on the River Hawksburgh, in 
Australia, discovered a nest of eggs in a small burrow that the Ornithorhynchus had just left. 
In a nest of twigs were nine eggs — more than has since been credited to the creature — of pecu- 
liar shape.” 
