,it present with Rondvorschen, is the furthest point 

 ihe dictionary has reached. The portion of the work 

 now pubhshed amounts to 14,469 pages (equivalent to 

 less than 6,000 pages of the Oxford Dictionary), and 

 contains about three-fifths of the Dutch vocabulary. 

 ***** 



The dictionary of the Swedish Academy is much less 

 advanced than either of the above. The first part 

 appeared in 1S93, and up to the present time four 

 complete volumes have been pubhshed, with portions 

 of another two. These, however, contain only the 

 letters A, B (incomplete), C, and D (incomplete) ; 

 five-sLxths of the Swedish vocabulary still remain to 

 be dealt with. 



***** 



In order to make the Oxford Dictionary accessible 

 to scholars and students, it is published at a price which 

 is at least as low as that for any printed matter in 

 book form. The price of a single section of 64 pages 

 is only 2s. 6d. net, or less than one halfpenny a page. 

 The entire work, so far as it has gone — the first nine 

 volumes bound in half-morocco, and the sections of Vol. 

 X in paper boards — can be purchased for £35 4s. td. net. 



Recent Work on Heredity 



By J. S. Huxley, M.A. 



Fellow of Kew College, Oxford 



(i) The Chromosomes .vs the Physical Basis of 



Heredity 

 The latest advance in general biology has been the 

 discovery that inheritance takes place by means of 

 separable units, generally known as unit-factors or 

 genes. It is effecting the same sort of revolution in 

 our biological thinking that Dalton's realisation of 

 atoms as the units composing chemical substances 

 did for chemical thinking a hundred years ago. 



But before we can grasp the meaning of this change, 

 we must go over some well-known facts of biology 

 that have been brought to light by microscopical 

 observation. Practically the whole of these facts 

 have been discovered in the last fifty years. Much 

 of the earlier work, especially on the meaning of the 

 observations, w£is done by Germans, prominent among 

 whom were Flemming, Weismann the great evolution- 

 ist, Boveri, and the botanist Strasburger. In later 

 years, England has produced well-known workers in 

 this field in the persons of Doncaster and Farmer, 

 and America in E. B. Wilson. The facts, as we 

 understand them to-day, are briefly as follows : 



All higher plants as well as higher animals, when 

 their tissues are examined under the microscope, are 



seen to be composed of visible units called cells. 

 Each cell consists of a mass of li\ang substance, the 

 cytoplasm, in which is embedded a central denser 

 body, also alive, the nucleus. .Although the number 

 of cells in the body of a man is to be reckoned not by 

 millions, but by millions of millions, they are all 

 formed during development from one single original 

 cell, the fertilised ovum. This starts by dividing into 

 two equal halves, then into four, and so on, growth 

 keeping pace with cell-division. When a cell divides, 

 its cytoplasm is simply split into two roughly equal 

 parts. The division of the nucleus is, however, a 

 more elaborate matter. The essential substance 

 condenses to produce a definite number of little threads 

 or rods, which take up many dyes, and are hence called 

 chromosomes, or coloured bodies. Every species of 

 animal and plant has a characteristic number of 

 chromosomes, and in any one species this number is 

 found in every cell. At division, each chromosome 

 is split down the middle, so that each single thread 

 gives rise to two new threads. One of these goes into 

 one of the two new cells formed by the division of the 

 old one, the other into the other. If we were to 

 imagine the chromosomes to consist of a series of 

 small units, of pieces of living substance, strung along 

 them like beads of different colours and shape along 

 a string, each one important in some way for life, and 

 each different from every other, then this peculiar 

 method of nuclear division by longitudinal splitting 

 of chromosomes would be an admirable way of en- 

 suring that all these different units should be divided 

 equally at each cell-division. In other words, each of 

 the two cells produced by division will get half of 

 every unit present in the original ceU ; and these 

 half-units, being composed of living substance, will 

 grow into wholes, so that all the millions of cells in 

 the body will possess a complete set of these units, 

 and one that is identical with the set which was present 

 in the original fertilised ovum. 



This fertiUsed ovum, however, did not arise out of 

 nothing. It was formed by the union of two cells 

 from the two parents. One, the unfertilised ovum, 

 was detached from the ovary of the mother ; the 

 other, the spermatozoon, was detached from the 

 reproductive tissue of the father. 



Here comes in a remarkable fact with regard to the 

 chromosomes. In any ordinary cell of the body, the 

 number of chromosomes is, speaking generally, an 

 even one. Sometimes the chromosomes of an animal 

 differ in size or shape, and when this is so they can 

 always be arranged in pairs, so that there are appar- 

 ently two sets of chromosomes, which may be compared 

 to two packs of cards. The ovum and sperm, however, 

 only contain half the ordinary number, and only one 

 of each pair — in other words, one whole set or pack. 



