in Li linm Martagon : If. Spermatogenesis . 2 1 7 
One important feature of heterotype karyokinesis is not 
represented in the diagrams. No indication is given of the 
long period of growth which ends in the formation of the 
spirem (G). The most prominent character of this period 
is the occurrence within it of the contracted state called 
synapsis, already twice described in detail. I believe the 
physiological purpose of this condition to be the formation 
of the spirem-ribbon from a single row of chromatin-granules 
strung on a linin-thread. This row is divided longitudinally 
just before the contraction begins, and during that con- 
traction the linin-ribbon, which separates the two rows of 
granules in the spirem-nucleus, is formed at the expense of 
the half-dissolved nucleolus (I, p. 458, and II, p. 198). 
The other features which distinguish heterotype from 
homotype divisions are fairly represented in the diagrams. 
They may be summarised here. 
Differentiation of the spirem-ribbon. In Diagram G, as. in 
A, the spirem-nucleus contains a coiled chromatic ribbon and 
one or more nucleoli within the nuclear membrane. But in 
A the ribbon appears to be homogeneous — its whole surface 
reacts in a uniform way to stains — and in G it is differ- 
entiated. The ribbon itself is erythrophilous, but it bears 
on either margin a row of cyanophilous granules. There 
may even be some further differentiation. At certain periods 
in the development of the ribbon, it seems as if the borders 
on which the granules lie were of rather tougher material 
than the broad zone which separates them. 
Early longitudinal fission of the chromosomes. In Diagram C 
the homotype chromosomes are seen to be formed of lengths 
of spirem-ribbon. Longitudinal fission follows later (D). In 
the heterotype nucleus the spirem-ribbon is first divided 
longitudinally and then falls into lengths. Thus each length 
consists of two separate linin-filaments, each bearing a single 
row of chromatin-granules (H). The nuclear membrane and 
nucleolus disappear before segmentation in the homotype 
nucleus (B), but persist for some time later in the hetero- 
type (I). 
