ORTHOPTERAN SPERMATOGENESIS 683 



same type of construction, but show a variety of shapes which are 

 constant in number. Thus in the Acrididae there are always 

 three rods, two very small and one medium in size; three crosses, 

 two of medium size and one large; and five rings or loops, four of 

 which are large and one of medium size. In Stenobothrus simi- 

 lar constant shapes, but in different numbers, occur. In every 

 case the chromosome is formed by the end union of spermato- 

 gonial chromosomes and, if unmodified, produces the simplest 

 type — the rod. If, at the point of union in such an element, the 

 parts diverge and becom.e extended at right angles to the length 

 of the rod, the cross is formed. Rings represent a union of the 

 two spermatogonial elements at both ends instead of at one as 

 in the other types. When the fiber attachment is not terminal, 

 as in Stenobothrus, there may be a lateral extension of the parts, 

 as in the rods, joined to a flexure at the point of fiber attachment 

 form_ing E-shaped chromosomes. (3) A gradual condensation 

 of the chromosomes carries the forms of the prophase over into 

 the metaphase. (4) In the first spermatocyte spindle the rods 

 are placed parallel to its length, the crosses with one arm in the 

 direction of the spindle axis and the other in the equatorial 

 plate, while the rings and loops are in such a position that their 

 free ends lie central and crossed with the synaptic ends directed 

 peripherally. According to the description homologous chromo- 

 somes should lie one above the other so that the opening of the 

 ring would be apparent from a lateral view, but in the few meta- 

 phase figures shovm (text fig. N) they appear clearly in polar 

 views. The figures of Stenobothrus, upon which form Davis 

 clearly has established his views, are much more numerous at 

 this stage and the rings are accurately shown lying extended in 

 the direction of the spindle axis. The other chromosomes appear 

 as in Dissosteira. (5) At the tim.e of chrom.atid separation the 

 halves of the extended rods merely move apart, showing first 

 a constriction at the point of division ; the crosses suffer a reduc- 

 tion of the lateral arms, due to an extension of their substance 

 into the vertical arms, and at length come to have the same 

 shape as the rods. The rings have their curved halves pulled 

 past each other in the axis of the spindle and at the end of the 



JOURNAL OF MORPHOLOGY, VOL. 25, NO. 4 



