A Cytological Study of the Semi-parasitic Copepod, Hersilia apodifnrmis etc. 401 



somes; and (2) to the presence of a "Querkerbe", or light transverse 

 streak marking each component of the bivalent chromosomes into two 

 parts. This "Querkerbe" was used as the most important evidence for 

 a pseudo-reduction of the chromosomes: it marking the point at which 

 two oögonial chromosomes remained in contact during the formation 

 of tlie oöcyte. The whole question of syndesis was very simple. The 

 chromosomes of the ultimate oögonial division formed a spireme which 

 segmented into half the normal number of chromatin bands, which 

 bands later showed their doubleness by a light transverse streak across 

 the middle. These double bands exhibited also a longitudinal division, 

 making thus four parts. Along this longitudinal division the chromo- 

 somes separated in the first division, whereas the second division was 

 at right angles to the first, and separated the chromosomes which had 

 been bound together by the linin bridge (Rückert '94a, '94b; Haecker 

 '95 a; vom Rath '95). 



Then Haecker ('95 b) discovered the presence of a second "longitu- 

 dinal division" of thle double bands, which made the chromosomes of 

 the first maturation division octads or di-tetrads. Both maturation 

 divisions were shown to be longitudinal, and later works (Braun '09; 

 Matscheck '10) have brought forth good evidence that the di-tetrads 

 do not divide at the "Querkerbe" in either division. These authors are 

 all supporters of an end-to-end conjugation of the chromosomes. Haecker 

 ('11) States his view in the following sentence (p. 328): "Die Querkerben^ 

 wie sie bei so vielen Objekten in den Prophasen der ersten Teilung wahr- 

 zunehmen sind, sprechen andererseits mit Entschiedenheit für eine Meta- 

 syndese." If the "Querkerbe" is to be used as an argument against 

 parasyndesis, then a careful study must be made to show how this structure 

 arises: whether (1) by a coupling of the (normal number) chromosomes 

 in the oögonia or spermatogonia, (2) by an incomplete segmentation of 

 the spireme (if such is ever formed) of the last oögonial or spemiatogonial 

 generation, or (3) by an end-to-end union of the chromosomes in the 

 growth period of the oöcytes or spermatocytes. 



If, on the contrary, we find that the "Querkerbe" is a constant 

 structure in the unreduced chromosomes of the somatic and germ cells 

 of animals belonging to widely separated groups (Copepods, Krimmel '10; 

 ?\ematodes, Marcus '06; MoUuscs, Zarxik '11; Vertebrates, Agar '11), 

 that the chromosomes never enter into a spireme, and that they pass 

 through those stages in the growth period which are so characteristic 

 of a side-by-side union, then the "Querkerbe" can no longer be used 

 as a positive proof for a metasyndesis. 



26* 



