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adjacent to the egg nucleus, apparently a centrosome formed from this nucleus. This aster is speedily transformed by division into a short spindle with a radiating aster at each end of it. If this spindle lies near enough to the surface of the egg to initiate a division furrow, parthenogenetic development may begin. It is interesting to observe, however, that the mitotic spindle formed by the nucleus of the unfertilized egg is only ⅘ of the length of the spindle formed by the fertilized egg, so that the size of the spindle is directly related to the number of chromosomes.

In the sea-urchin's egg the primary stimulus, which is usually momentary immersion in a fatty acid (such as butyric), only produces an aster on which the chromosomes are distributed but which is unable to metamorphose itself into a spindle. If, however, the eggs are subsequently immersed in "hypertonic" sea water that is, sea water in which the percentage of salt is raised above the normal amount, then one or more accessory asters are formed in the cytoplasm. Whence the particles arise which act as centrosomes for these asters has never been ascertained; that they have previously been emitted from the nucleus is a pure assumption. If only one accessory aster has been formed a mitotic spindle is formed between it and the aster which arises round the egg nucleus. On to this spindle migrate the chromosomes. A regular equatorial plate is formed, and division of the nucleus and of the whole egg ensues and development is initiated. As the accessory aster is usually smaller than the primary egg aster, the two blastomeres into which the egg divides are of unequal size, and we thus learn that the size of the daughter cells into which a given cell divides is related to the relative sizes of the asters at the two poles of the spindle.

Conclusion.— From the foregoing sketch the reader will gather that the science of cytology had attained in 1921 an extremely interesting stage of development. New discoveries had poured in, the exact significance of which was not yet fully understood, and although we had glimmerings of light they serve rather to pose than to answer questions. What, for instance, is the significance of the mitochondria and the Golgi apparatus? They surely must have some very important function in cell life, for the more research is pushed the wider seems to be their distribution. They have been recorded from Protozoa and from tissue cells of both animals and plants, as well as from eggs and spermatozoa, yet the only function which so far can definitely be assigned to them is the production of transient structures in the ripe spermatozoon. What is the meaning of the centrosome, and how is it related to the formation of astral rays? It cannot be detected in the living cell and yet the study of stained cells would lead us to regard it as a permanent cell organ typically outside and independent of the nucleus and, like the nucleus, handed on by division from a cell to the daughter into which it divided. Yet, as we have seen, it can be formed de novo in the cytoplasm by the action of hypertonic sea water and Lillie^[1] has shown that it can be formed de novo from the nucleus. In the fertilization of the eggs of the annelid Nereis the spermatozoon penetrates the egg membrane but slowly. Lillie centrifuged eggs in which the head had penetrated but in which the middle-piece with the centrosome were still left outside and he succeeded in tearing away the middle-piece altogether. After the cessation of the centrifugal force the mutilated head completed the penetration of the egg and developed a new centrosome by the emission of a particle from itself which was just as effective in forming the first spindle as the original centrosome.

The astral rays and the mitotic spindle are formed by the gelation of the cytoplasm; yet their formation is dependent on the activities of the chromosomes; for an unfertilized egg responds to stimulation not only by the production of an aster but by the resolution of its chromatin into chromosomes, and the length of the spindle which is formed is dependent on the number of chromosomes.

The nucleus must in some way control the growth of the cytoplasm, and genetic experiments indicate (see Genetics) that each type of chromosome has a particular function to play in the building-up of the embryo, yet the only emission from the nucleus which has so far been detected has been that of nucleolar material.

Finally, the constitution of living cytoplasm seems to be normally that of a thick colloid solution, which at times changes

 

1. F. B. Lillie," Studies on Fertilization in Nereis," III. and IV., Jour. Exp. Zoöl. vol. xii. (1912).

to that of the gel condition. It baffles our imagination, however, to conceive how a solution can be the seat of internal structure and how in particular a nerve cell, with all its inherited and acquired aptitudes or "engrams," can be in life nothing more than a thick syrup.

References.—W. E. Agar, Cytology, with special reference to the Metazoan Nucleus; A. Brachet, "L'Œuf et les Facteurs de l'Ontogenèse," Encyclopédie Scientifique (1916); L. Doncaster, Textbook of Cytology (1908) ; E. B. Wilson, The Cell in Development and Inheritance (1906).(E. W. MacB.)

CZECHOSLOVAKIA (Čiskoslovensko, Čiskoslovenská Republika). The republic of Czechoslovakia is a new creation in respect of its name and state-form only. Its modern history as an independent entity begins with the dramatic collapse of the Austro-Hungarian Monarchy at the close of the World War, and the definitive proclamation of Czechoslovak independence on Oct. 28 1918. Some of its constituent territories, however, notably Bohemia and the lands of the Bohemian crown (Moravia, Silesia, Lusatia) enjoyed, up to the year 1620, many centuries of independent existence and played an important, sometimes a dominating, part in the political and religious history of central Europe.

The republic has a pop., according to the census of 1921, of 13,595,818, and an area of about 55,000 sq. m. (approximately the size of England and Wales). It comprises three great natural regions: (1) Bohemia, (2) Moravia and Silesia, (3) Slovakia and Russinia (Sub-Carpathian Russia=Podkarpatská Rus). Bohemia, with an area of some 20,400 sq. m., has a pop. of 6,664,932; Moravia, with 8,600 sq. m., 2,660,737 inhabitants; Silesia, 1,800 sq. m., and 670,937 inhabitants; Slovakia, 20,000 sq. m., and 2,993,479 inhabitants; Russinia, 5,000 sq. m., and 605,731 inhabitants. The whole is about 600 m. long and has a maximum breadth of 185 miles. In respect of population it occupies the tenth place among European countries; in respect of size the fourteenth place; in density of population the seventh.

The frontiers were fixed by the Peace Treaties of St. Germain, Versailles and Trianon, while a portion of the ancient principality of Těšín (Teschen) was adjudicated to it by the Paris Conference (July 1920). On the W. and N., where it borders upon Bavaria, Saxony, Prussia and Poland, it is enclosed by mountains, some of them of very considerable height, which form on those sides a natural and strategic frontier. In Bohemia the highest peak Sněžka (Schneekoppe) has an altitude of 5,216 ft., in Slovakia the summits of the Carpathians and of the High Tatra rise to a height of between 7,000 and 8,000 ft. South of these ranges lie fertile and well-watered plains and lowlands extending to the borders of Austria, Hungary and Rumania. Some 60% of the entire area of the republic is included in the basin of the Danube, the rest being traversed by the Labe (Elbe) and the Vltava (Moldau), the former passing in particular through regions remarkable for their rich fertility. Some one-third of the entire surface of the country is covered by forests. The climate of the republic is a medium between a maritime and continental one.

Prague, the capital (677,000 inhabitants), is picturesquely situated on the Vltava and justly famous for its architectural beauty. Bratislava (Pressburg), the capital of Slovakia, with its great Danubian harbour, is the gateway of central European trade to the East and the Balkans. Other towns of importance in the republic are Brno (Brünn), with 200,000 inhabitants, the capital of Moravia, and the centre of an old established and flourishing textile industry; Plzeň (Pilsen) with 100,000 inhabitants, famous for its beer and as the seat of the Škoda iron works; Košice (Kaschau), the commercial centre of eastern Slovakia; and Užhorod (Ungvár), the capital of Russinia. Of German towns in Czechoslovakia (most of them with a considerable Czechoslovak minority), Liberec (Reichenberg), and Jablonec (Gablonz), are important industrial centres. Carlsbad (Karlovy Vary), and Marienbad (Mariánské Lázně), are famous spas. Czechoslovakia indeed is one of the richest states of Europe in mineral and health-giving waters, and possesses more than 200 watering places and health resorts. Besides Carlsbad and