" heterotypical" mitosis in nereis limbata. 69 



Up to eleven hours after the fertilization a longitudinal split 

 may be clearly visible in the terminally (or.subterminally) attached 

 daughter chromosomes, this split being as in the first matura- 

 tion division identical with the space between the two branches of 

 a metaphase-halfring or, which is the same, between the two 

 diverging arms of the horseshoe-shaped chromosomes of the 

 prophase. 



With regard to this period, therefore, it will be enough to men- 

 tion the characteristics through which each division, or group of 

 divisions, is distinguished from the other ones (comp. the chrom. 

 of the different divisions on pp. 62-63). 



Second Maturation Division. 



In the eggs of Nereis there is no resting stage between the two 

 maturation divisions, the formation of a new spindle taking place 

 even before the first polocyte is fully separated from the egg-cell. 

 The chromosomes, therefore, pass directly from the telophase of 

 the first division into the prophase of the second, and no great 

 changes are seen to take place in their structure (see p. 62, 2nd 

 mat. div.). 



The chromosomes of the prophase are mostly V- or horseshoe- 

 shaped with a longitudinal split and attached by their middle 

 point. There are however also found cross-shaped ones with 

 four equally long arms being attached by their center on the sur- 

 face of the spindle. In the metaphase we find the chromosomes 

 arranged in a circle round the equator of the spindle, their form 

 being through an approach of the diverging arms, transformed 

 into a rodlike one. In a few cases I have seen a tetrad-like struc- 

 ture of these chromosomes (chrom. 12, p. 63) a fact which is in 

 complete harmony with their genesis and with the appearance of 

 a longitudinal split in the daughter chromosomes. 1 



1 (Added on the proof-sheet, June, 1907.) With regard to a similar doubleness 

 of the chromosomes shown by me (1905, '06) in Enteroxenos, A. and K. E. Schreiner 

 express themselves as follows (1907, p. 18): 



"Weder die Beobachtungen Bonnevie's von dem Vorhandensein einer solchen 

 Doppelheit der Chromosomen, noch ihr Versuch, dieselbe mit der in der I. Reifungs- 

 teilung sichtbaren zu vergleichen, sind neu ; vielmehr gibt es schon iiber diese Frage 

 eine ganze kleine Literatur, die aber von Bonnevie nur geringe Beobachtungen ge- 

 funden hat." 



They then mention the observations of Ed. van Beneden (1883) and Flemming 



