354 PRESENT PROBLEMS IN EVOLUTION AND HEREDITY. 

 LECTURE III. — HEREDITY AND THE GERM CELLS. 



Accord iug" to the general law* the gerai cell was cousiderecl as 

 matter potentially alive and having within itself tlie tendency to as- 

 sume a definite living form in course of individual development. The 

 nucleus must be extraordinarily complex, for it contains within itself 

 not only the tendencies of the present type, but of past types far 

 distant. The supposition of a vast number of germs of structure is 

 required by the phejiomena of heredity; Niigeli has demonstrated that 

 even in so minute a space as one one-thousandth cubic millimeter, 

 400,000,000 micelhe must be present. 



The study of heredity will ultimately center around the structure and 

 functions of the germ cells. The precise researches of Galtou show 

 that the external facts of heredity, questions of average and of proba- 

 bilities, of paternal and maternal contributions to the oftsprings, are 

 capable of being- reduced to an exact science in which mathematical 

 calculations will enable us to forecast the characteristics of the coming- 

 generation. 



There will still remain however a large residuum of facts which will 

 present themselves to a mathematician like Galton, as fortuitous, or in- 

 exact, such as the physiological conditions of reversion; the course of 

 pre-i)otency, by which the maternal or the paternal characteristics pre- 

 vail in parts or in the entire structure of the offspring; the material 

 basis of latent heritage upon which reversion depends, and which com- 

 pels us to hypothecate either an unused hereditary substance or a return 

 to an older disposition of the forces in this substance; the nature and 

 determination of sex. These apparently chance phenomena must also 

 be due to certain tixed laws, and by far the most promising routes to 

 discovery have already been taken by Van Beneden, the liertwig 

 brothers, Boveri, Maupas, and others. 



They have attacked the problem of the relation of the germ cells to 

 the heredity on every side, and by the most ingenious and novel meth- 

 ods, which are familiar enough in various branches of gross anatomical 

 and i)hysiological research, but seem almost (mt of the limits of applica- 

 tion to minute microscopic objects. For example, the Hertwig brothers 

 have ascertained the intiuence of various solutions of inorpidne and 

 other drugs of the alcohols, and of the various degrees of temperature 

 upon the ovum and spermatozoon during- the conjugation period, witli 

 results wliicli are highly suggestive of the causes of congenital mal- 

 formations, anomalies, and double births. The Hertwigs and Boveri 

 have succeeded in robbing ova of their nuclei and watching- the results 

 of the subsequent entrance of spermatozoa. In order to further test 

 the relations of the nucleus to the remainder of the cell, Verworn has 

 experimented along the same Hue with extirpations of every kiml from 

 the single cells of Infusoria. Of equal novelty are the recent studies of 



"See Huxley, Article "Evolution," Enc. Britannica, vol. viii, p. 746. 



