" HETEROTYPICAL MITOSIS IN NEREIS LIMBATA. 8 1 



more natural to consider the longitudinal split of the anaphases 

 merely as an unusually narrow space between the two arms of 

 V-shaped daughter chromosomes, and the cross-shaped chro- 

 mosomes of the prophases as arisen through a precocious sepa- 

 ration of the daughter chromosomes, connected or crossing each 

 other on their middle point. The same view must be held also 

 with regard to the maturation and the later cleavage divisions, 

 the tetrads, so often met with, being considered as merely mor- 

 phological structures, arisen through an approach of the two 

 arms of a V, that is, their two longitudinally split halves, a and 

 a must be looked upon as forming one continuous ribbon, sharply 

 bent on its middle point. The point of attachment of the chromo- 

 somes would, from this point of view, in all divisions be a median 

 one, the many cases in which a terminal attachment seems to be 

 shown, being explained as artefacts. 



As will be seen from the above, each of these interpretations 

 meets with difficulties, which at the present state of our knowledge 

 interferes with the acceptation of any of them. 



In order to solve these difficulties it will be of great im- 

 portance to follow the changes in the mode of attachment of the 

 chromosomes throughout the whole germ track — and especially 

 to compare the chromosome-relations of species in which a 

 median attachment of the chromosomes seems to be predominant 

 {Tomopteris, Salamandra, etc.), with those of other species, in 

 which the chromosomes are terminally attached to the fibers. 



In my following papers I shall publish my first results of such a 

 comparative study, and even if the solution of the problem of 

 maturation is still far away, I hope to be able to throw some new 

 light on the question. 

 Columbia University, 

 March, 1907. 



LITERATURE. 

 Beneden, Ed. van. 



'83 Recherches sur la maturation de l'oeut et la fecondation. Arch, de 

 Biol., T. 4. 



Bonnevie, Kr. 



'05 Das Verhalten des Chromatins in den Keirazellen von Enteroxenos oster- 

 greni. Anat. Anz. , Bd. 26. 



'06 Untersuchungen iiber Keimzellen. I. Beobachtungen an den Keimzellen 

 von Enteroxenos ostergreni. Jen. Zeitschr., Bd. 41. 



