46 STUDIES IN SPERMATOGENESIS. 



later (fig. 241) when the nucleus has enlarged and the spireme has 

 become looser and stains less deeply. Here the odd chromosome is 

 more condensed, or shortened, and split. There is no synizesis and 

 no polarized or bouquet stage, but the nuclei of all of the spermato- 

 cytes contain a continuous spireme throughout the growth stage. 

 Synapsis must occur at the close of the last spermatogonial mitosis 

 before the spireme is formed. Figures 242 and 243 show a slightly 

 later growth stage. The form and connection of the "w-chromosome" 

 pair (Wilson, '051,) comes out clearly here. Figure 244, from a safranin- 

 gentian preparation, shows both the odd chromosome and the m- 

 chromosomes. Some time before the first mitosis, the spireme splits 

 and the pairs of granules embedded in linin are wonderfully distinct, 

 both in iron-haematoxylin and safranin-gentian preparations (fig. 

 245). The w-chromosomes have here formed a precocious tetrad (m). 

 Figure 246 is a similar stage from a safranin-gentian preparation. Fig- 

 ures 247 and 248 show the condensation of chromatin granules to form 

 tetrads of various sizes, still embedded in the linin spireme. As these 

 tetrads come into the spindle without losing their elongated form, it is 

 evident that each one consists of two longitudinally split chromo- 

 somes united end to end in synapsis and separated in the first matura- 

 tion mitosis, which is therefore reductional. The odd chromosome 

 and the w-chromosomes show no longitudinal split in these figures, 

 but they may appear as in figure 249. Occasionally one of the tetrads 

 takes the form of a cross (fig. 249). In this figure the split " acces- 

 sory " (V) lies against the nuclear membrane and the archoplasmic 

 material for the spindle is seen along one side of the nucleus. It is 

 certain here that the spindle fibers come from extranuclear material, 

 not from nuclear substance, as Paulmier ('99) describes for Anasa 

 tristis. 



Figures 250 and 251 show the first maturation mitosis as it usually 

 appears in sections from mercuro-nitric material stained with iron- 

 hsematoxylin . The odd chromosome is always more or less eccentric 

 and is attached by a spindle fiber to one pole. In Hermann material, 

 considerably destained, the tetrads and the odd chromosome appear 

 as in figures 252, 253, and 254, the tetrads being in position for a trans- 

 verse division. The odd chromosome is always so placed that its lon- 

 gitudinal split is at right angles to the axis of the spindle, as though 

 it were to divide in this mitosis. It does not do so, however, but 

 goes to one daughter cell, always lagging behind, as is shown in 

 figures 255 and 256. Figures 257, a and b, are polar plates of the 

 first mitosis with n and 12 chromosomes, respectively, and fig- 

 ures 258, a, d, and c, show the polar plates (a and c) each containing 



