OOGENESIS AND EARLY EMBRYOLOGY ASCARIS 547 



but he believes that they are produced by the folding on itself 

 of a single longitudinally split chromosome. Hertwig ('90) 

 alone favored the telosyndesis view. 



In A. canis, by a like process of parasyndesis, as I have stated, 

 one eight-parted chromosome is formed out of two tetrad chro- 

 mosomes. Marcus ('06), working on A. canis (?), found similar 

 eight-parted chromo'somes, but he believed them to be formed 

 by the telosyndesis of two chromosomes, each of which later 

 showed two longitudinal splits, in planes at right angles to each 

 other. These chromosomes Marcus designates as bivalent te- 

 trads or octads. Greg6ire ('10) has pointed out that, as the 

 chromosomes are the result of a pseudo-reduction process, the 

 term ' octad' is a misnomer, for the resultant eight-parted chromo- 

 somes are in reality not two conjugated (that is involving syn- 

 mixis) chromosomes, but only two loosely joined, semi-inde- 

 pendent tetrads, and he suggests the name ' di-tetrad' as a better 

 appelation. In accordance with this conception, the term di- 

 tetrad, instead of the term octad, is used throughout this paper 

 to denote the eight-parted chromosomes of the prophase and 

 metaphase of the first maturation division. 



The same type of chromosome is formed in the spermato- 

 cytes (Walton, '16 a), but there, the process of formation could 

 not be followed clearly enough to show that the method of union 

 is by parasyndesis; yet the similarity of the process in the sper- 

 matocytes to that in the primary oocytes is so close as to force 

 one to conclude that the method of formation is the same in 

 both sexes. After the union the di-tetrad chromosomes look like 

 tetrads in either a side or a polar view (fig. 24), but by careful 

 observation the plane of union between the two tetrads can be 

 seen to be unlike that of the cross and longitudinal constrictions 

 of the original tetrads (text-fig. A, 5 b). 



The presence of eight-parted chromosomes has been reported 

 for several Nematodes, and by Jorgensen ('10) in sponges (Sy- 

 conen). Bonnevie ('08) describes a faint indication that the 

 chromosomes of A. megalocephala before the first maturation 

 division (Muttertetradeii) are really octad in nature, and are 

 reduced to tetrads by this division. She finds the same to be 



