498 THE AMERICAN NATURALIST. [VOL. XXXIX. 



during the metaphase of the heterotypic but a fundamental dif- 

 ference in the accounts of the manner in which these structures 

 are formed. 



In conclusion, we may very briefly note the fact that the 

 zoologists are divided into two schools in their accounts of 

 reduction phenomena, apparently along similar lines to those 

 of the botanists. Some recent papers (Winiwarter, : oo ; 

 Schoenfeld, :oi ; and the Schreiners, -.04) have described the 

 union of parallel threads (maternal and paternal) during synapsis 

 to form a single spirem in the rabbit, man, bull, hag-fish, and 

 shark. Winiwarter and the Schreiners regard a later longitudi- 

 nal fission of the spirem as a separation of the two threads 

 which originally entered into the structure. The chromosomes 

 in the hag-fish (Myxine, the Schreiners, : 04) are organized in 

 pairs side by side and a second longitudinal split appears in 

 each. The heterotypic mitosis separates the groups in the plane 

 of the first fission and the two parted chromosomes are divided 

 by the homotypic. This history is essentially similar to Allen's 

 account of the lily. On the other hand there is a large body of 

 observations founded on the investigations of Hacker, vom 

 Rath, Riickert, Montgomery, and others, indicating that bivalent 

 chromosomes are formed consisting of somatic chromosomes 

 joined end to end and that these elements or their derivatives 

 are distributed either with the heterotypic or homotypic mitosis. 

 This of course involves a transverse division which is, however, 

 interpreted as the separation of adjacent chromosomes and not 

 as a qualitative division in Weismann's sense. The attitude of 

 the first group is clearly similar to that of Allen, Rosenberg, 

 Berghs, and Gregoire among the botanists, while that of the 

 second shows many points of similarity to the theory of Farmer 

 and Moore and to Strasburger's last view (: 04). There are a 

 number of accounts of a double longitudinal fission of chromo- 

 somes especially among the vertebrates, which have not been 

 harmonized with the last view but may find explanation along 

 the lines of the more recent investigations. 



It is of course conceivable that there are two distinct types of 

 arrangement of sporophytic and somatic chromosomes in animals 

 and plants at synapsis during gametogenesis and sporogenesis. 



