700 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Wilms), but they are its reduced sisters or brothers, identical with it in 

 ultimate characters. They never arise from cells which at any time 

 may be regarded as cells of the individual. Exactly as identical twins 

 are the products of two sister or brother germ-cells, identical in ancestry 

 from the same primitive germ-cell, and alike in all ultimate characters, 

 so also any animal and a tumour within it — say, a sarcoma or tumour of 

 embryonic tissue — stand in the same relations of ancestry from one 

 primitive germ-cell, and have the same ultimate characters at the starting- 

 point of their development. But, unlike fully developed identical twins, 

 the individual and its tumour develop in different directions : the one 

 upwards along the track of higher and higher organisation, the other 

 downwards along the roadway of abnormality, of degeneration, of arrest, 

 at times even of riot, destruction and disaster. 



Cause of Inverse Symmetry.* — Edwin C. Conklin brings forward 

 some indirect evidence in support of the thesis that inverse symmetry — 

 in man, in snail, in threadworm, &c. — is due to a reversal of the polarity 

 of the liberated ovum. Such a reversal entirely and satisfactorily ex- 

 plains all the phenomena of inverse symmetry in embryonic and adult 

 stages, whereas no other explanation does this even approximately. But 

 if the reversal of polarity at the time of maturation can bring about a 

 total inversion of all parts of the embryo and adult, then there must 

 be a definite localisation of germinal primordia or " Anlagen " in the egg 

 before maturation, e.g. the substance out of which the kidney of the 

 snail will ultimately form must be definitely localised on one side of the 

 chief axis, and so for every other part. If the inversion of the egg at 

 the time of maturation inverts the position of every part which develops 

 from it, no more convincing evidence could be found that "organ- 

 bildende Keimbezirke " are present and definitely localised in the im- 

 mature egg. 



Mendelian Heredity .f — W. Bateson calls attention to various possi- 

 bilities attainable by a modification of the Mendelian method. His 

 facts relate to the crossing of rose-comb and pea-comb poultry with 

 single combs. His theme, in general terms, is the Mendelian heredity 

 of three characters allelomorph ic to each other. 



Embryonic Development of Mammalian Ovary and Testis.} — 

 Bennet M. Allan gives a preliminary account of researches on the de- 

 velopment of the ovary and testis of the rabbit and pig. The con- 

 stituent elements of these structures in origin and development are 

 compared ; seminiferous tubules, medullary cords, and rete cords are 

 found to be homologous. No evidence has been found favouring the 

 theory of the early segregation of sex-cells, yet the author is not pre- 

 pared to say that his work in any way tends to disprove such a theory. 

 There are some interesting facts bearing upon questions concerning the 

 action of trophic stimuli in embryonic development. The most striking 

 example of this is the formation of follicles in the portion of rete 

 tissue within the ovary, while the extra ovarian part is not so affected. 



* Anat. Anzeig, xxiii. (1903) pp. 577-88 (8 figs.). 

 + Proc. Cambridge Phil. Boo., xii. (1903) pp. 153-4. 

 t Biol. Bulletin, v. No. 1, pp. 55-G2. 



