262 Cytologie und Befruchtung. 



The aiithors briefly consider the chief views that have been 

 held as to the nature of reduction in animals and pbnts. They 

 point out that the widely accepted view of the occurrence of 

 two longitudinal fissions of the chromosomes in the maiotic 

 phase is not oniy inherently improbable, but also impossible 

 to reconcile with the facts (e. g. those obtained by the study 

 of hybrids) which point so strongly to the individuality of the 

 chromosomes or at least of some form of discrete particles con- 

 cerned in heredity. Furthermore such a mode of fission affords 

 no satisfactory explanation of the peculiar series of changes 

 constantly recurring in the heterotype and homotype (i. e. 

 maiotic) mitoses of animals and plants. It is further pointed 

 out that the extreme orderliness, constant occurrence and 

 general similarity of the heterotype mitosis suggest the great 

 importance and the real identity of the process in animals and 

 plants, so that some reconciliation must be possible between 

 the various conflicting views. In support of this view the 

 authors have investigated the maiotic phase in Lilliim candi- 

 diim, Psilotum triquetnim, Osmiinda regalis, and Aneiira pin- 

 giiis among plants, and Periplaneta orientalis, several Elasmo- 

 branch and Amphibian types, the mouse, rat and man among 

 animals. In all these forms the authors find that the hetero- 

 type chromosome is formed from a portion igenerally split 

 longitudinally) of the original spireme thread, which portion 

 becomes beut over to form a loop; it is the space between 

 these portions which has so constantly been mistaken for a 

 fission. The bivalent heterotype chromosome then becomes 

 divided transversely at the bend and the two portions (usually 

 exhibiting the early longitudinal split) move to opposite poles 

 in the first maiotic mitosis. Each chromosome of the hetero- 

 typic division is thus bivalent and represents two somatic chro- 

 mosomes. The essential peculiarities of the maiotic phase can 

 thus be explained as „due to the coherence in pairs of pre- 

 maiotic chromosomes and the intercalation of a special form 

 of chromosome distribution during the course of what would 

 otherwise not differ materially from an ordinary pre-maiotic 

 mitosis. In the first of these two divisions a distribution of 

 entire pre-maiotic chromosomes is secured and thus the number 

 of these bodies is really halved. In the second division the 

 longitudinal division, began, but temporairly arrested, in the 

 preceding prophase, takes effect". The peculiar shapes of the 

 heterotype chromosomes are related not to two longitudinal 

 fissions but to the looping of the spireme thread combined 

 with one longitudinal fission. 



These conclusions being based on a broad foundation in 

 both kingdows are put forward as general for animals and 

 plants. They receive support from the carly observations — 

 for a long time isolated — of Korscheit on Ophiyotroclia, those 

 of Montgomery on certain animals and the work ofStras- 

 burger on Galtonia published since the appearance of the 



