Cell Changes in the Testis due to X Ravs. 
253 
cells remains a spermatogonium, while the other becomes a spermatocyte 
of the first order. 
The spermatocytes of the first order undergo a series of changes 
which terminate in what is known as the first maturation division (hetero- 
type or fkrst meiotic division). These changes are briefly as follows. 
The masses of chromatin seen in the young cell become distributed along 
linin threads which make their appearance in the nucleus (Fig. 4). These 
threads become more and more nnmerous until eventually the nuclear 
chromatin is arranged in a fine network 1 ). This network now becomes 
gradually coarser, and ultimately forms a spireme, this condition being 
brought about by the disappearance of the finer connecting Strands of 
the network (Figs. 5 and 6). The spireme threads shorten and form the 
heterotype chromosomes or gemini. These are of various shapes; loops, 
rings and rods 2 ). In the meantime, the two centrosomes originally present 
in the archoplasm leave the latter and migrate to opposite sides of the 
nucleus, a spindle being formed between them. The nuclear membrane 
now breaks down and the chromosomes become attached to the spindle 
fibres (Fig. 7). The chromosomes next move apart to the respective poles, 
and the formation of the daughter cells, which are termed spermatocytes 
of the second order is soon completed. An archoplasm (Figs. 5 and 6) 
appears quite early in the young spermatocyte, and continues visible 
until division occurs, after which it becomes lost in the cytoplasm and 
can no longer be distinguished. The nucleolus makes its appearance in 
the spermatocyte of the first order at an early stage, when the chromatin 
is still in the condition of a fine network 3 ). There is also present in the 
nucleus at this stage the intranuclear body or plasmosome. Both the latter 
structures remain visible until the nuclear membrane disappears. 
The spermatocytes of the second order present a nucleus with a 
sparse network of chromatin and a well marked nuclear membrane (Fig. 8). 
Jn the cytoplasm is seen the archoplasm and a structure called the chroma- 
toid body, representing the remains of the nucleolus of the spermatocyte 
of the first order. The chromatoid body is again met with in the spermatid 
shortly to be described ; its presence in the cytoplasm of these two classes 
of cells is of aid in distinguishing them from spermatocytes of the first 
order. A definite spireme such as is seen in spermatocytes of the first 
order is not formed, but the chromatin network breaks up into a number 
of short rods, which, becoming smaller and more compact, form the 
!) Cp. Duesberg (1), Figs. 6 — 9. 
2 ) Cp. Duesberg (1), Fig. 17. 
3 ) Cp. Duesberg (1), Fig. 7. 
