MUNSON: SPERMATOGENESIS OF PAPILIO. 
71 
while the proximal half grows and divides alternately, giving rise thus 
successively to a series of primary spermatogones. 
At the same time one or more cortical nuclei (pi. 15, fig. 57, Jc) are 
pinched off with the primary spermatogones and become the cyst 
cells (pi. 15, fig. 58). 
The nucleus of the primary spermatogone is large and regularly 
spherical. The cytoplasm is not especially abundant. The cyto- 
reticulum is distinct. At one pole of the nucleus an irregular mass of 
archoplasm can be seen when properly stained (pi. 15, fig. 58). 
Period o) multiplication .— When the spermatogone prepares for 
division the chromatin of the nuclear reticulum is aggregated into 
spherical chromosomes, arranged near the periphery. There are 
twenty-eight chromosomes. They preserve their individuality to a 
remarkable extent throughout the history of the cell. 
The archoplasmic mass elongates and finally divides, each half 
moving to opposite poles of the nucleus (pi. 15, fig. 59), where two 
large asters, with minute but distinct centrosomes, are developed. 
The nuclear membrane disappears while the nucleus is being con¬ 
verted into a spindle with the chromosomes at the equator (pi. 15, fig. 
60). The spherical chromosomes are then split and each half is 
drawn towards its respective pole (pi. 15, fig. 57a, e). The metaphase 
and the telophase are most frequently seen, the prophases and ana¬ 
phase being passed through rapidly. The details of the prophases 
are more readily made out in maturation, where they are described 
more fully. The chromosomes having reached their respective poles, 
the cytoplasm constricts through the equator of the spindle, forming 
two equal cells which owing to the persistence of the intermediate 
fibers remain united for some time (pi. 15, figs. 61, 62). The chromo¬ 
somes then begin to separate owing to the formation of karyolymph, 
a new nuclear membrane appears (pi. 15, fig. 63), the intermediate 
fibers gradually disappear, and the two-celled stage is attained (pi. 15, 
fig. 64). 
They are surrounded by the cortical cells (pi. 15, fig. 64), which 
also divide a few times by karyokinesis, forming a distinct spindle 
like that just described (pi. 12, fig. 4, a, /). I infer that these cortical 
cells, now the cyst cells, divide only in this early period, because I 
have never seen them divide in the larger and more developed cysts. 
A second division of the two spermatogones (pi. 15, fig. 64) soon 
ensues, leading to the four-celled stage (pi. 15, fig. 65). During their 
