WHAT makes the formless egg or germ become organized into the fully developed animal or plant in other in other words, what is the cause of embryonic differentiation? That is at present one of the most difficult questions of biology. A discovery of far-reaching importance, which may well prove as fundamental in the field of development as did the discovery of the circulation of the blood in physiology, or of segregation in genetics, has recently been made by the German zoologist Spemann.

In the course of a long series of painstaking researches upon the development of the newt he has perfected a technique which enables him to play the most amazing tricks upon the eggs and embryos. For instance, one of his pupils, Mangold, has been able to unite two developing eggs of two different species of newt into one, which proceeded to develop into a single normal embryo in spite of its chimeric composition!

Spemann himself, however, has been able to discover something more fundamental to wit, the cause of differentiation. The fertilized egg of a newt, like that of most other animals, at first consists of a round mass of living substance containing a nucleus, and laden with a considerable quantity of yolk and other material destined for the needs of the embryo which will develop from it. No definite structure even remotely resembling that of the adult is to be seen; the various substances, such as yolk, fat, and so forth, which are

often more dense at one pole than at the other, seem only to be raw materials for the constructive processes which are to take place later.

The next step is the division of the egg into two, four, eight, and so on till several dozen or (in the newt) several hundred small cells have been produced from the original large one. Then, in the newt and other amphibia, a new process occurs. At one place near the equator of the egg, the smaller, less yolk-laden cells begin to multiply more rapidly and to grow down as a fold or flap over the larger yolky cells. The infection, so to speak, spreads sideways; so that as the fold extends downward it enlarges laterally, its free edge becoming at first crescentic, then semicircular, then horseshoe shaped, and finally circular. The circle diminishes until at last the whole of the yolky part has been overgrown. The edge of the fold is called the lip of the blastopore.

Directly after this the first signs of differentiation become apparent. The side on which the fold first appeared becomes the back, for here appears a thickening which soon becomes converted into the rudiment of the brain and spinal cord. Below this the notochord, forerunner of the backbone, is formed, and on either side the rudiments of the muscles. The cavity of the digestive tube appears below the notochord, and the kidneys on either side. In a very short time the rudiments of all the chief organs of the future tadpole are blocked out: differentiation

MAPPING NORTHERN GREENLAND

To protect its Eskimo subjects from the twin evils of civilization, drink and disease, the Danish Government has kept such close guard over most of Greenland that even now little is known of its topography. The last number of the English scientific monthly, Discovery, prints an interesting article by Mr. H. T. Shepstone describing the adventurous exploration of Dr. Lauge Koch, whose map-making expedition took him 3600 miles over ice of the most dangerous sort, and resulted in a survey of unmapped parts of the

coast.

The expedition was financed from both public and private funds. Its chief, Dr. Koch, has spent eight years in Greenland engaged in exploration and other scientific work, and was a member of Knut Rasmussen's second expedition which filled the gaps in the map of the east coast as far as the De Long Fjord. Dr. Koch set out to carry the survey clear up to Cape Bridgman, in the remotest part of Peary Land. His expedition started out in March 1921 with nineteen sledges, two hundred dogs, a few tried and tested Eskimos, and Dr. Koch himself, the only European. Most of the time the temperature stood at 40° below zero. At Etah five sledges had to be sent back. At Fort Conger on Grand Lake the party picked up provisions which had been left the year before by Captain Roald Amundsen. The expedition pushed on to 80° north latitude, where the auxiliary sledges were sent back to the base and the number was cut down to four men, three sledges, and thirtytwo dogs. Four days later they passed the most northerly point that the Rasmussen expedition had reached in

1917. Here they divided, two Eskimos being sent off to hunt and accumulate fresh meat, while Dr. Koch and a single Eskimo went up the coast to survey. The mapping was finished on the morning of Whitsunday on the latitude of 83° 5". It was the most northerly point ever reached by the Danish flag.

The return journey was perilous, the hunting expedition having secured nothing but fifty-three hares and a wolf. They ran into a snowstorm which lasted a fortnight, exhausted most of their provisions, and were forced to pull on the ropes to assist what dogs were left. When things were at their worst they ran into a herd of musk oxen and replenished their supplies. The entire expedition was nearly wiped out in crossing the Petermann glacier, but came through with all their men, though by this time only four dogs were left. A heavy gale from the north enabled them to hoist sails on their sledges and skim over the ice to a point where they could see their heap of reserve provisions through their field glasses. One of the dogs died of starvation within sight of the food.

Dr. Koch regards his geological results as very important. He has brought back four thousand geological specimens, including animal fossils dating from very early periods, and both European and Western-American forms. The public, however, will probably regard his map-making as his most important work.

SUMMER OPERA

BAYREUTH, Munich, and Vienna have vied with one another this summer in their opera seasons. At Bayreuth the semiofficial, semisacred production of the Ring was carried out with extraor

dinary perfection in some respects, marred by extraordinary flaws in details where one might have looked for something on a par with the whole. The Bayreuth conductor was Herr Hans Bahling, who is universally lauded for the extraordinary tone and perfect accuracy which he and his players achieved. The critic Max Marschall writes from Bayreuth to Die Vossische Zeitung in Berlin; 'Bahling is an orchestral conductor who demands the utmost in perfect and subdued tone, yet brings out each detail with perfect clarity and unusual emotional liveliness.'

Sad to say, however, not all the singers were up to the high standard of the chorus and orchestra. Herr Eduard Habich, who has an English as well as a German reputation, sang Alberich with great success. London critics wired their praises home, and Herr Marschall declares his Alberich 'famos.' Herr Lorenz Melchior received high praise from some critics as Siegmund, but Herr Marschall insists that his inclusion in the cast was 'a dangerous experiment, and experiments- especially dangerous ones are the last thing that the director of a festival production ought to attempt.' There were complaints that the Brunnhilda, Fräulein Olga Blomé, was simply not capable of her task. The stage mechanisms of the nineteenth century - which are gradually becoming offensive to audiences accustomed to modern methods that leave more to the imagination and yet demand less credulity of the spectator somewhat marred the perform

ance.

At Munich there was a distinct feeling of competition with Bayreuth. In contrast with the stern economy of Wagner's theatre, the Prinz Regenten Theater in Munich is a sumptuous opera-house, but with acoustics which scarcely compare with those that Wagner achieved, whether by good luck or

good management, in his own famous but unpretentious theatre. The chorus and orchestra are said to have fallen below the standard of Bayreuth, although the conductor, Herr Hans Knappertsbusch, is not without praise from the critics. Some of the singers, particularly Herr Joseph Geiss as Beckmesser, are accused of descending to mere buffoonery. Yet an English critic telegraphs that Geiss 'gave an extraordinarily good performance.'

In Vienna Mascagni conducted a performance of Aïda out of doors before an audience of more than twenty thousand. In spite of acoustic difficulties that seem almost insurmountable, it is said that not even the pianissimo parts of the overture were lost and that Zenatello's voice filled the whole amphitheatre.

Mascagni has been asked to go to England, but complains that ‘the impressarios always ask me to conduct Cavalleria Rusticana. My other children are never asked for. On these terms I refuse to go. If they will listen to my beloved Iris and the Piccola Mara I will gladly go.' At Vienna the secret leaked out that he is contemplating a return to composition and that the Opéra Comique in Paris has engaged him to do a new opera which is based on a novel of Emile Bergerat. A French playwright is now at work on the book. The title is to be Plus que Reine.

RAISING CALIGULA'S GALLEYS AT the bottom of Lake Nemi, in the heart of the Alban Hills, where once stood a famous sanctuary and grove of Diana, lie two galleys which were fitted out as floating palaces of pleasure for the Roman Emperor Caligula. Their magnificence was beyond even the most palatial yacht of to-day. Incrusted with marbles, ornamented with