322 THOS. H. MONTGOMERY, 



with small aperture and thick wall (Figs. 167, 170, 172, 174, 178, 185). 

 The definitive ring has lost the longitudinal split, and frequently ap- 

 pears to be a perfect ring in as much as there may be no constrictions 

 on its surface to mark the positions of the ends of the two univalent 

 chromosomes; but we shall see that the position of their distal ends 

 may be still recognized by the points of attachment of the persisting 

 distal linin fibres. This type of chromosome is represented in diagram 

 255, Plate 25. 



4) Chromosomes of quadripartite form (Fig. 183). The only two 

 cases of such chromosomes seen by me were in the monaster stage, 

 when the definitive form is reached, so that I have not observed 

 their mode of origin. Such a chromosome has a more or less rhom- 

 boidal shape, and is formed of 4 separate chromatin rods. I think it 

 probable that such a chromosome represents a union of two bivalent 

 chromosomes, so that each of its component rods would be a uni- 

 valent chromosome. This is not a surprising conclusion, since every 

 two bivalent chromosomes are connected by a distal linin fibre. The 

 supposed origin of such chromosomes is represented in diagram 256, 

 Plate 25. 



All the types of chromosomes, with the exception of the very 

 rare one last described, are clearly bivalent, each composed, just as in 

 the synapsis and telophase preceding, of two univalent chromosomes 

 whose central ends are joined by the central band of linin. My 

 classification into several types is, however, an arbitrary one, in order 

 to facilitate the description, for there are no sharp lines of demarcation 

 between these types, as a study of the carefully drawn Figs. 134—174 

 will show. My deductions as to the evolution of each type from the 

 early prophase to the monaster were made by pieciug together, and 

 arranging in as natural a manner as possible, the different forms 

 observed. In the early prophases no two chromosomes show exactly 

 the same form, but in my figures practically all the main forms have 

 been reproduced. The deductions as to the lines of evolution of these 

 difierent forms have been concisely expressed in diagrams 253 — 256 

 of Plate 25. 



The early stages in the prophases are of the greatest importance 

 in determining the exact constitution of the chromosomes of the 

 1st maturation division : the composition of them could not at all be 

 determined by a mere examination of their definitive forms found in 

 the monaster stages (Figs. 177—182, 184—188). It is only in the 

 early prophases that the chromosomes have a constitution that can 



