STENOPELMATUS. 7 



and, moreover, all of the spindles and all of the spermatids appear to 

 be exactly alike at the same stage. The chromosomes are double in 

 the prophase (fig. 77) and always appear double in the equatorial plate 

 (fig. 78), the paired elements corresponding to those of figure 65. 



In figure 80, plate in, a pair of spermatids is shown with nuclear 

 membrane formed and the spindle fibers twisted in a characteristic 

 manner. Figure 81 is a slightly later stage with the spindle-remains 

 massed against the nuclear membrane. Curiously enough there 

 appears in the nucleus of every spermatid a body similar to the element 

 x of the spermatocytes of the first order (figs. 82-86). This body is 

 often applied to the nuclear membrane and connected with the spireme 

 (figs. 84-86). It decreases in size and finally disappears (figs. 88-91). 

 The spindle-remains divides (fig. 83), and a small part of it (a) goes to 

 form the acrosome at the apex of the head (figs. 85-92). The larger 

 part is probably utilized in the formation of the tail, for it gradually 

 disappears as the tail develops. 



The centrosome which, although small, is conspicuous in each 

 mitosis, is seen in figure 83 between the two parts of the spindle- 

 remains, applied to the outside of the nuclear membrane. In figures 

 85, 86, and 87 the relation of the tail (or its axial fiber) to the centro- 

 some is shown. In figures 87 and 88, instead of the small spherical 

 centrosome of figures 83 to 86, we have a much elongated body, at 

 first (fig. 87) applied for its whole length to the nuclear membrane, but 

 later lying along one side of a middle piece (m), as shown in figure 89, 

 and in a later stage in figures 90 to 92. The mature spermatozoon 

 with its forked anterior end appears in figure 93. 



The points of especial interest in the spermatogenesis of Stenopel- 

 matus are the development of the aberrant chromatin element x during 

 the growth stage of the spermatocyte of the first order, its distribution 

 to one-half of the spermatocytes of the first order, its disappearance 

 during the rest stage between the two maturation divisions, and 

 the development of a similar, though smaller, element in all of the 



spermatocytes. 



Blattella germanica. 



Unlike the spermatogonia of Stenopelmatus ', those of Blattella have 

 both a faintly-staining nucleolus and a deeply-staining chromatin 

 element (x), and moreover the two are always closely associated (figs. 

 95, 96). The number of chromatin elements in the equatorial plate 

 of late spermatogonial mitoses is 23 (fig. 97). Later events indicate 

 that one of the 23 is the element x, but it is impossible to distinguish 

 it here. Figure 98 is a very early stage of the spermatocyte of the first 

 order, showing the element x as a U-shaped body. The centrosome 



