498 |. THE AMERICAN NATURALIST. | [Vor. 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 
zoólogists are divided into two schools in their accounts of 
reduction phenomena, apparently along similar lines to those 
of the botanists. Some recent papers (Winiwarter, :00; 
Schoenfeld, :01; 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 thelily. On the other hand there is a large body of 
observations founded on the investigations of Häcker, vom 
Rath, Rückert, 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 Grégoire 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. 
