GENERATION AND INHERITANCE 301 



And now there occurs a second striking variation from the usual 

 process of nuclear and cell-division. While otherwise, after division, 

 the nuclear substance always passes for a time into the spherical 

 resting state, here it immediately prepares itself for a second divis- 

 ion, which leads to the cutting-off of a second polar cell. The half 

 of the first polar spindle remaining in the egg (Fig. 3, sp) immediately 

 enlarges itself into a second complete spindle, in whose middle the 

 two dyads lie. These immediately separate into their individual 

 dements, of which two are taken up into the second polar cell 

 (Fig. 4, pz"*), and two remain in the egg, and here form the basis of 

 the egg-nucleus. Thus of the entire chromatin mass of the egg- 

 nucleus which was divided into eight chromosomes, the mature egg 

 only contains the fourth part, that is, from each of the two tetrads 

 only one single chromosome (Fig. 4, eik, ch). Instead of once, as 

 in usual cell-division, the chromatin has been divided twice by two 

 polar divisions; in other words, it has been quartered. Therefore, 

 the egg-nucleus only contains half as much chromatin as the nucleus 

 of an ordinary tissue-cell or an embryonal cell. Immediately after 

 each division, it is, to a certain extent, only half a nucleus, and as 

 such is an exception to the numerical law of chromosomes. Weis- 

 mann has called the whole process, by which is effected the reduction 

 of the nuclear mass and the number of chromosomes to half, a "re- 

 duction division." 



As the sperm-nucleus in Ascaris only possesses half the number 

 of chromosomes of a normal nucleus, the conclusion may be drawn, 

 that in it also a reduction must have occurred, as occurs in the 

 egg by the formation of the polar cells. By such consideration, I was 

 led to seek for a corresponding process in the formation of sperm, 

 which premise showed itself as correct. 1 



As an accurate comparison of the egg- and sperm-formation in 

 Ascaris shows, there exists in the two a complete parallel, which 

 may be followed into the smallest detail. The unripe egg with a 

 spherical nucleus, the egg mother cell or ovocyte (Diagram m, 

 Fig. 1), corresponds to the sperm mother cell or spermatocyte 

 (Diagram iv, Fig. 1), as each undergoes a reduction by the forma- 

 tion of polar cells. Also the chromatin arranges itself in the nucleus 

 in this extremely characteristic way which is observed nowhere ex- 

 cept in sexual cells in two groups of four each (Diagram iv, Fig. 1 ch.) 



1 Even before my investigation Platner determined by a study of the process of 

 sperm-formation in Lepidoptera and Pulmonata a reduction process in the sperm- 

 nuclei, although in a less striking and less comparative way. He drew the conclusion 

 "the spermatocytes correspond to the ova. In both cases a reduction of the 

 chromatic substance to a quarter of its original quantity occurs, while a second 

 division follows immediately on the first without a period of rest between." (Plat- 

 ner, On the Meaning of the Polar Bodies, Biologisches Centralblatt, vol. vui, p. 193, 

 1889, and Contributions to the Knowledge of the Cells and their Division, Arch, fur 

 mikrosk. Anat., vol. xxxin, 1889.) 



