GERM-CELL HISTORY IN THE BROOK LAMPREY 61 



the oogonia. According to these investigators, synapsis may 

 take place previous to synizesis, and the two phenomena proba- 

 bly have nothing in common. Most investigators, however, 

 agree that the double nature of the chromosomes is first visible 

 during a late stage of the heterotypic prophases, but their inter- 

 pretations of the doubling vary. Some consider it a suppressed 

 mitosis (Hertwig, '08; Matscheck, '10, and others), while the 

 majority of workers on germ cells look upon it as a pairing of 

 parental chromosomes similar to that which takes place in the 

 male germ cells previous to the maturation division. Very little 

 light can be thrown upon this subject by the lamprey, since it 

 was found impossible to count the chromosomes before or after 

 synapsis. To all appearances, however, the chromosomes enter 

 synizesis in the univalent condition. The bivalent nature of the 

 chromosomes is not observable before the diplotene stage. 



The meaning of the 'contraction figure' has been variously 

 interpreted. Some investigators consider it simply an artifact due 

 to poor preservation (Janssens, '05; Jorgensen, '10, and others). 

 Marechal and Saedeler ('10) insist that it is not an artifact in 

 Raja clavata. King ('08) has shown that it is a perfectly normal 

 condition in the toad. In the lamprey it appears to be a normal 

 phenomenon, and forms a stage in the morphological changes 

 which take place in the oocyte at this time. In the same gland 

 were cells in the contraction phases, other cells in the various 

 stages of the synapsis phase, normal resting cells, and cells in 

 the different phases of mitosis. Degenerating cells also occurred 

 in most glands, but no evidence was found to indicate that the 

 contraction figure is a phase in the process of degeneration. Even 

 in the same cyst, there are contraction figures side by side with 

 resting cells and cells in other stages of the synapsis phase. It 

 must be c'oncluded, therefore, that the phenomena connected with 

 synizesis in the lamprey are perfectly normal and due to some 

 peculiar condition of the cells at this time — a condition the nature 

 of which is not yet understood. 



Whether the contraction figure is normally formed around the 

 nucleolus or on the side next to the centrosome could not be deter- 

 mined. A body sometimes occurs in the cytoplasm near the 



