1 84 



FERTILIZATION OF THE OVUM 



These discoveries were confirmed and extended in the case of 

 Ascaris by Boveri and by Van Beneden himself in 1887 and 1888 

 and in several other nematodes by Carnoy in 1887. Carnoy found 

 the number of chromosomes derived from each sex to be in Coronilla 

 4, in OpJiiostoimim 6, and in Filaroides 8. A little later Boveri 

 ('90) showed that the law of numerical equality of the paternal and 

 maternal chromosomes held good for other groups of animals, being 

 in the sea-urchin Echinus 9, in the worm Sagitta 9, in the medusa 

 Tiara 14, and in the mollusk PterotracJica 16 from each sex. Similar 

 results were obtained in other animals and in plants, as first shown by 

 Guignard in the lily ('91), where each sex contributes 12 chromosomes. 



A ^ 



Fig. 91. — Germ-nuclei and chromosomes in the eggs of nematodes. [Carnoy.] 

 A. Egg of nematode parasitic in Scyllium ; the two germ-nuclei in apposition, each containing 

 four chromosomes; the two polar bodies above. B. Egg of Filaroides ; each germ-nucleus with 

 eight chromosomes ; polar bodies above, deutoplasm-spheres below. 



In the onion the number is 8 (Strasburger) ; in the annelid Ophryo- 

 trocha it is only 2 from each sex (Korschelt). In all these cases the 

 number contributed by each is one-ha/f the jwniber characteristic of the 

 body-cells. The union of two germ-cells thus restores the normal 

 number, and here we find the explanation of the remarkable fact 

 commented on at page 67 that the njiniber of chromosomes in sexually 

 prodjiced organis^ns is alzvays even} 



These remarkable facts demonstrate the two germ-nuclei to be in 

 a morphological sense precisely equivalent, and they not only lend 

 very strong support to Hertwig's identification of the nucleus as the 

 bearer of hereditary qualities, but indicate further that these qualities 



1 Cf. p. 67. 



