366 The Spermatogenesis of Bufo Lentiginosus 
and one longitudinal division of the chromosomes, as the individuality 
ot the chromosomes is lost if two equation or two transverse divisions 
oceur. 
Sebaschnikoff’s (5) re-examination of the ovogenesis of Ascaris has 
made it doubtful whether, after all, the tetrad groups are here formed 
by a double longitudinal division; Boveri (4) and Montgomery (40) 
have more recently brought forward strong arguments in favor of the 
occurrence of a reduction division in the germ-cells of Ascaris; and 
Strasburger (58), after a re-examination of his material, is now of the 
opinion that a reduction division also occurs in the higher plants. It 
remains only to bring the investigations on the germ-cells of the am- 
phibians into line with these later investigations on other forms to 
establish the rule that there is one reduction and one equation division 
in the maturation of the germ-cells of all animals and plants so far 
investigated. There is, apparently, a great diversity in the way in which 
reduction is accomplished in the various forms. 
Most of the investigators who have worked on the spermatogenesis 
of the Urodela agree that, in the early prophases of the first maturation 
division, the reduced number of chromosomes appears in the form of U- 
or V-shaped loops; and they have tacitly assumed, if not expressly 
stated, that each loop is a bivalent structure being composed of two 
chromosomes united end to end in synapsis. Later these chromatin 
loops split longitudinally and the sister-portions of each loop remain 
united at the ends, opening up through the middle to form ring-shaped 
chromosomes. In metakinesis the rings are said to be placed on the 
spindle in such a way that the plane of the union of the two halves of 
the chromosomes lies in the equator of the spindle. The heterotypic 
division which follows separates sister-portions of the longitudinally split 
chromosomes and is therefore an equation division. In the anaphase 
the V-shaped chromosomes again split longitudinally preparatory to the 
second maturation mitosis which is also an equation division. 
Montgomery, who is a firm advocate of the view that the first matura- 
tion mitosis must necessarily be reductional, has investigated the pro- 
phases of the first maturation division in the spermatocytes of two am- 
phibians, Plethodon and Desmognathus, and his interpretation of the 
ring-formation in these forms differs considerably from that given by 
Meves, McGregor, and Hisen(11). In the early prophase of mitosis, 
Montgomery also finds the reduced number of chromosomes in the form 
of loops which he considers to be composed of two chromosomes united 
end to end in synapsis; each arm of a loop representing one chromo- 
