PREDETERMINATION OF SEX 311 



napsis in other forms does not in any way resemble the process 

 that she describes as such. Xhe four figures that Miss Stevens 

 gave to illustrate the stage in question are quite inadequate to 

 establish this interpretation. Von Baehr also dissents from Miss 

 Stevens' view. 



In parthenogenesis the relation between reduction in number 

 of the chromosomes and the occurrence or non-occurrence of the 

 synapsis stage has been studied in a few forms. Woltereck in 

 1898 examined the oogenesis of a species of ostracod, C'ypi'is rep- 

 tans, known to breed by parthenogenesis, and showed that the 

 eggs have a distinct contraction stage ('synapsis'). Prior to this 

 condition the chromosomes thicken and then condense at one 

 side of the nucleus. When they emerge, the full number is 

 present, i.e., there has been no reduction through pairing of the 

 chromosomes. Since this change takes place at the time when 

 the ordinary synapsis would be expected, there is a presumption 

 in favor of the view that the contraction figure corresponds in 

 some regards at least to the synapsis stage. 



Schleip in 1909 studied both parthenogenetic and sexual spe- 

 cies of ostracods. In both a synapsis stage was found from which 

 in the parthenogenetic species the full number of chromosomes 

 emerge; while in the sexual species the reduced number of chro- 

 mosomes appear. 



Kiihne in 1908 described a stage at the beginning of the growth 

 period in the parthenogenetic phyllopod, Daphnia pulex, in which 

 the chromosomes contract and concentrate in radial lines around 

 the nucleohis. He compares this condition with the synapsis 

 stage described by Woltereck, but thinks that the evidence here 

 does not suffice to establish the identity of the two. The total 

 number of chromosomes appears later, without any evidence 

 that there has been pairing. 



Fries in 1909 found no synapsis stage in the phyllopod, Arte- 

 mia salina, which reproduces by parthenogenesis. The egg and 

 the body cells coritain the fvill number of chromosomes. In 

 Branchipus, on the other hand, which reproduces by means of 

 sexual eggs, there is a usual synapsis stage, followed by reduction 

 in the number of the chromosomes. 



