633 



Untersuchungen der letzten Jahre stimmen darin überein, daß schon 

 vor der ersten Reifungsteilung Chromatinportionen auftreten, deren 

 Zahl die Hälfte beträgt von der Normalzahl der Chromosomen der 

 betreiFenden Species«. Prof. Haecker's former views coincided with 

 these; and to-day, ten years after Rück e rt's Referat, we can say that 

 pretty general uniformity has been reached in this matter. But Prof. 

 Haecker (1902) has recently completely changed his opinion again. 

 According to his present view there is no reduction in number of chro- 

 mosomes preceding the first maturation division, but after this division 

 there takes place a reduction in number by a pairing of the chromo- 

 somes in the second ovocyte. Thus there would be 12 chromosomes, 

 in the first ovocyte, 6 bivalent ones in the second, and 6 bivalent ones 

 in the ovotid. The 12 chromosomes of the first polar spindle are said 

 to be arranged in two groups of 6 each, each group corresponding to 

 a gonomere of the germinal vesicle; each of the 12 is segmented both 

 longitudinally and transversely, and is therefore bivalent. In the first 

 division each is halved equationally, so that each second ovocyte re- 

 ceives 12 bivalent chromosomes, each of which has a transverse but 

 no longitudinal split. Before the arrangement into the equator of the 

 second polar spindle "these 12 bivalent chromosomes conjugate to 

 form 6 (the before quadrivalent) chromosomes. As he states (1904. 

 p. 192): »Es entstehen H- oder X-förmige Figuren, welche demnach je 

 aus einem Chromosom zusammengesetzt sind. . . Bei der zweiten Thei- 

 lung treten diese neugeformten bivalenten Elemente aus einander. . . 

 Demnach erhält schließlich der Eikern 6 bivalente Elemente, welche 

 je aus einer väterlichen und einer mütterlichen, oder, da die reife Ei- 

 zelle bereits eine neue Generation repräsentiert, aus einer großväter- 

 lichen und großmütterlichen Hälfte besteht.« 



It is with a feeling of much reserve that I would critizise obser- 

 vations on an object which I have not personally studied. I would not 

 for an instant doubt Prof. Haecker's statement of facts, but this is a 

 question of interpretation, and in matters of interpretation all obser- 

 vers may sometimes go wrong. These results are so much at variance 

 with the conclusions on Vertebrates, Insects, Peripatus and Polyclades, 

 that it would seem there must be either some error of interpretation, 

 ore else that the particular ova studied showed pathological conditions. 

 No w in the first place in his » Praxis und Theorie «(1899) Prof. Haecker 

 states (p. 172) that the normal number of chromosomes in Cyclops 

 hrevicornis is 24, that there are 12 in the earlier generations of the 

 germ cells and 6 in the ovotid. But Rückert found for other related 

 Copepoda, as has been found indeed for most objects, that the normal 

 number is the same for somatic cells and the earlier generations of the 



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