322 KING. [Vol. XVII. 



Langspaltung der Chromosomen im Dyaster der letzten Teilung 

 des Ureies." 



After the formation of the first polar spindle in the egg of 

 Bufo, the subsequent longitudinal splitting of the chromatin 

 rings can be definitely proved (PI. XXIX, Fig. 25). Hence, 

 assuming the rings to be originally composed of two sister- 

 halves of a split chromatin thread, both polar divisions are 

 " equal divisions " and there is no qualitative division of the 

 "ids " as Weismann's theory demands. 



In the results obtained by Boveri ('87) on Ascaris, ('90) on 

 Petrotrachea and other mollusks ; by Brauer ('89) on Branch- 

 ipus, ('93) on Ascaris ; by Hertwig ('90) on Ascaris ; by Moore 

 ('96) on elasmobranchs ; and by Meves ('97) on Salamander, 

 there is manifestly a disagreement with the reduction process 

 as described by Weismann ('85, '92), in that the tetrad groups 

 arise from a double longitudinal division of primary chromatin 

 rods, and not from one longitudinal and one transverse division. 



Guignard ('9i) and Strasburger ('94) have stated that there 

 is no evidence of a transverse division of the chromosomes in 

 flowering plants. They find only a reduction in the number 

 of chromosomes, which is brought about by a segmentation of 

 the spireme thread into one-half the usual number of chromo- 

 somes. These chromosomes do not form tetrads, but undergo 

 simple longitudinal splitting at each succeeding division. 



Equally strong evidence in favor of the Weismann hypoth- 

 esis has been given by vom Rath ('92, '93, '95) from an exhaust- 

 ive study of the tetrad groups in Salamander, Gryllotalpa, and 

 various copepods ; by Henking ('91) from his work on insects ; 

 by Hacker ('95) and Riickert ('93, '96) from investigations on vari- 

 ous copepods ; and by Calkins ('97) from a study of the tetrad 

 formation in Pterodophytes. According to vom Rath, there is 

 first a longitudinal splitting of a primary chromatin rod, the 

 ends then unite and open out to form a ring, which subse- 

 quently breaks into four parts by a separation of the two halves 

 corresponding to the original longitudinal splitting, followed by 

 a second transverse division of each half. The latter is the 

 "reduction division," by which there is a qualitative division of 

 the chromatin substance. 



