PROCESS OF FERTILIZATION IN THE CRAB 1S 
A general statement of spermatogenesis 
There persists along one side of the tubule a single row of 
cells with large nuclei, the division of which give rise to the 
spermatogonia. The latter multiply irregularly to form a large 
mass which, in transverse sections, has the shape of a crescent. 
At first cell walls can be made out, but later the nuclei seem to 
lie in an undivided mass of cytoplasm. Gradually the division 
of these nuclei ceases and a spireme is formed within each of them. 
The division up to this time has taken place without the for- 
mation of any spireme structure. The appearance of the latter 
is the first indication that the cells have reached the spermatocyte 
stage. After the spireme has been formed the nuclei pass into 
synapsis which lasts for a comparatively long time, so that all 
the nuclei in a considerable portion of a tubule will be found in 
this stage at the same time. After synapsis, cell walls are formed 
in the cytoplasm which persist up to the anaphase of the first 
maturation division. In the nucleus the chromosomes are formed 
and the maturation divisions follow one another in quick succes- 
sion. They begin at one end of the tubule and pass along it 
like a wave, so that the spindle-figures are found in only a small 
section of the tubule at any given time. While these events are 
taking place within the tubule the cells in the wall of the latter 
multiply so that the wall becomes considerably thickened. The 
primary spermatogonial cells also divide to start a new group of 
spermatogonia. Between these cells and the spermatocytes there 
is always a layer of epithelial cells which persist to form the 
partitions between the two successive batches of seminal ele- 
ments. The mass of spermatogonial nuclei remains small until 
the spermatids are well advanced in their transformation into 
spermatozoa. : 
As the mass of spermatogonia increases, the developing sperma- ~ 
tozoa are crowded more and more to one side of the tubule. 
These spermatozoa reach their mature state before the second 
batch enter synapsis. The epithelial cells surrounding the mature 
spermatozoa, we may suppose, secrete a fluid which, together 
with the increasing mass of spermatogonia, press the mature 
