38 STUDIES IN SPERM ATOGENESIS. 



dumb-bell and ring-shaped bivalents (figs. 65-67). In preparations 

 much destained (fig. 67) the small chromosome component of the 

 group retains the stain longer than the larger one. The spindle in 

 prophase (fig. 68) is much elongated and the '8 chromosomes are often 

 spread out upon it so as to be easily counted. In the early metaphase 

 the parachute-like heterochromosome group is always nearer one pole 

 of the spindle (plate x, figs. 69 and 70). The equatorial plate often 

 shows both the larger component of the pair and the plasmosome (fig. 

 71). Figures 72-74 show the metakinesis of the heterochromosome 

 bivalent. In figure 74 the two unequal elements are completely sepa- 

 rated and the plasmosome has disappeared. The equatorial plates of 

 the two resulting kinds of second spermatocytes appear in figures 75 

 and 76. In the anaphase of the second division all of the chromo- 

 somes are divided quantitatively as may be seen in figures 77 and 78. 

 A few dividing male somatic cells were found in the walls of the 

 testis. Figure 57 (plate ix) is an equatorial plate from one of these. 

 The chromosomes are like those of the spermatogonia (figs. 58 and 59), 

 15 large and i small. No dividing female somatic cells were found. 

 A few drawings of developing spermatids are given to show the 

 transformations of a peculiar body which seems to be characteristic of 

 insect spermatids. Figure 79 is a very young spermatid showing only 

 diffuse chromatin in the nucleus. The nucleus soon enlarges (fig. 80) 

 and a large dense body (n) appears which stains like chromatin with 

 various staining media. A little later (fig. 81) the chromatin forms 

 a homogeneous, more or less hemispherical or sometimes crescent- 

 shaped mass which stains an even gray in iron-hsematoxylin. In 

 addition the nucleus contains a body (n) smaller than in the preceding 

 stage, but staining the same. As the nucleus condenses and elongates 

 to form the sperm head, a light region containing this deeply staining 

 body is seen on one side (figs. 82, 83). A little later the body is 

 divided into two, which appear sometimes spherical (fig. 84), some- 

 times elongated (fig. 85). As the sperm head elongates still more, 

 approaching maturity, these bodies diminish in size (figs. 86, 87) and 

 ultimately disappear. A cross section of the sperm head at such a 

 stage as figure 87 shows the chromatin in crescent shape with material 

 which stains very little within (fig. 88). The chromatin -like body 

 described above was observed in Tenebrio in a stage corresponding to 

 figure 81, and it was thought that the larger body seen in some cases 

 and the smaller one in others might be the larger and smaller hetero- 

 chromosomes, but a study of this element in more favorable material 

 disproves that supposition by showing that the different sizes are 

 merely different phases in the evolution of the body. Throughout its 



