1892,] Heredity and the Germ- Cells. 643 
phenomena must also be due to.certain fixed laws, and by far 
the most promising routes to discovery have already been 
taken by Van Beneden, the Hertwig brothers, Boveri, Maupas, 
and others 
They have attacked the problem of the relation of the germ- 
cells to heredity on every side, and by the most ingenious and 
novel methods, which are familiar enough in various branches 
of gross anatomical and physiological research, but seem 
almost out of the limits of application to minute microscopic 
objects. For example, the Hertwig brothers have ascertained 
the influences of various solutions of morphine and other 
drugs, of the alcohols, and of various degrees of temperature 
upon the ovum and spermatozoon during the conjugation 
_7-—Tyercat CELL Division, SHOWING THE DISTRIBUTION OF CHROMATIN. (From Par- 
ter, ‘tees Carnoy ) A-C, Arrangement of the chromatin in threads ; D-E, Formation of the chro- 
in rods and loops; F, Splitting of the loops; G-H, Retraction of the chromatin into the two 
ccc 
period, with results which are highly suggestive of the causes 
of congenital malformations, anomalies, and double births. 
he 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 line with extirpations of every 
kind from the single cells of Infusoria. Of equal novelty are 
