8 
W. E. AGAR. 
distinct from that of the spermatogonia. The chromatin is in 
the form of an extremely fine meshwork, without any large 
blocks at all (PI. 1, fig. 8). There is a single large nucleolus 
(not visible in fig. 8, but shown in fig. 9), which is very 
characteristic of this stage. 
The Meiotic (Maturation) Divisions. 
Nomenclature. — For the various stages of the pro phase 
I have used the nomenclature now generally adopted, based 
on that proposed by von Winiwarter in his work on mam- 
malian oogenesis. The stages run: leptonema, zygo- 
nema, pachynema, strepsinema or diplonema 
(adjectives leptotene, zygotene, etc.), and diakinesis. 
In pachynema the chromatin threads are arrauged in the 
characteristic bouquet grouping. The one-sided contraction 
of the chromatin may occur at any of the above stages — in 
Lepidosiren it begins in the sirepsitene stage. In order to 
avoid the confusion caused by the word “ synapsis,” I have 
here employed Mr. Clung’s term synizesis for the visible 
clumping together of the chromatin, and Hacker’s word 
syndesis for the conjugation of the chromosomes. 
The most important stages in the maturation divisions are 
shown in the text-figure. 
First Meiotic Division. — The first indication of the 
approaching mitosis is that the dense reticulum of the resting 
primary spermatocyte gradually gives way to a condition in 
which certain principal threads can be recognised and followed 
for a considerable distance, and this gradually changes into 
the leptotene stage in which all the chromatin is in the form 
of very long fine threads, which twist about and cross one 
another in a most complicated way. A nucleus in this stage 
is shown in PI. 1, fig. 9. The fine threads are so numerous 
and involved that, in order to avoid confusion, I have only 
figured those threads which lie immediately below the nuclear 
membrane in one hemisphere. In reality the whole volume 
of the nucleus is filled with the tangle of threads. It should 
