CHROMOSOME STUDIES 225 



three V's, and Haecker himself has also shown V's ('11, figs. 22, 

 30, 65). 



But we do not always find V's in the copepods as described 

 by Haecker, Matscheck and others. This is possibly due to the 

 fact that the limbs of what might be regarded as straightened- 

 out V's are usually so short that they have a tendency to lie 

 in one axis instead of at an angle to each other, and also that in 

 some of these species there may be few compound chromosomes. 

 The V structure, if present, appears in anaphases, whether the 

 limbs are short or long. Lerat's cells were evidently in the 

 right stage to show V's. 



The best evidence of the compound nature of the chromosomes 

 in Copepoda is the presence of a constriction, leaving an archo- 

 plasmic bridge, median or submedian in position, which gives 

 to the chromosome the appearance of being transversely seg- 

 mented. Lerat denies the presence of the constriction or break, 

 but admits the presence of a non-staining region. His figures, 

 however, show constrictions at the apices of the V's. This 

 segmentation has been figured by Riickert ('93), Schiller ('09, 

 figs. 7-19), Haecker ('95, '02), Krimmel ('10) and Matscheck 

 ('10). Riickert (see Lerat, '05, p. 181) was the first to describe 

 the phenomenon of segmentation in chromosomes, though prob- 

 ably he did not understand its meaning. Haecker ('11, p. 45) 

 describes this phenomenon when he says, ''Seltener ist eine durch 

 helle Querkerben hervorgerufene wirkliche Segmentierung wahr- 

 zunehmen, so z. B. bei den 'bivalenten' Chromosomen der Kope- 

 poden (fig. 14b) und offenbar auch bei den auffallend langen 

 'Sammelchromosomen' von Ascaris." He has, however, in 

 my opinion, misinterpreted this bridge as representing a stage 

 in the reduction process, in accordance with his metasyndesis 

 theory, which postulates that at some time during the life cycle 

 of the animal after fertilization of the egg and before the first 

 maturation division takes place, there occurs an end-to-end 

 synapsis of like chromosomes, resulting finally in a fusion during 

 the growth stages of the first maturation cell. It will be seen 

 that, according to Haecker, the transverse segmentation of 

 chromosomes in the Copepoda does not persist as a permanent 



