Erik Nordenskiold 
163 
these three parts of the spermatid must be specially studied. This develop¬ 
ment is characterized by a still more considerable elongation of the nuclear 
rod. The internal end of it begins to bend in various directions (Figs. 12-16). 
The external end of the nucleus also assumes a characteristic shape, its point 
becoming bluntly elongated, almost club-shaped (Figs. 15-18). This end 
retains its position at the surface of the nucleus, and forms the fixed point, 
round which the other parts of the nuclear rod move; the latter is sometimes 
S-shaped, sometimes spiral-shaped. As development proceeds the rod becomes 
progressively thinner and more convoluted. 
Parallel to this development of the nucleus there are equally important 
changes in the plasma. The endoplasma, as we left it, when it had reached 
the cell membrane in the neighbourhood of the external end of the nucleus, 
extends its surface from this point and grows in this way all around the 
ectoplasma (Figs. 10, 12, 16-18). And at the same time the above-described 
endoplasmatic projection, opposite the internal end of the nucleus, penetrates 
deeper into the ectoplasma and assumes a more pointed shape (Figs. 14, 15, 17). 
In the protuberance there accumulates a considerable quantity of mito¬ 
chondria from the endoplasma, the whole projection acquiring a deep colour 
(Fig. 17). With this mitochondrial body the internal end of the nucleus enters 
into a relation, thus making it most difficult to observe the development of 
the centrosome in the phase that now follows. 
As the internal end of the nucleus begins its movements, the centrosome 
follows them. It is often seen in the first stages of the bent nucleus at the 
concave side of the rod, the concavity of which seems to be occupied by the 
clear zone round the centrosome (Figs. 11, 12). Later on the centrosome 
seems to become attached to the end of the nucleus and surrounded by a now 
very diminished clear zone (Fig. 14). Thus situated, it follows for a while 
the movements of the nucleus as shown by Fig. 16. But after this it is soon 
lost to sight. At the same time we see that the end of the nucleus extends 
into the mitochondrial body of the endoplasma (Figs. 15, 17) and therefore 
we may conclude that at this phase the centrosome leaves the nucleus 
and remains among the mitochondria. It is not possible to adduce any strict 
proof of this statement, since, as is mentioned above, it is impossible to 
decolourize the mitochondria in a way that leaves the centrosome stained. 
Nevertheless this supposition is very probable. The loosening of the connection 
between nucleus and centrosome happens at the same time as the nucleus 
and the mitochondria come into contact, moreover, the mitochondrial body 
in the succeeding development plays a part scarcely intelligible without 
assuming union with the centrosome. This being the case it will be assumed 
in the following that the above statement is correct. 
The next stage of the spermatogenesis effects an ejection of a part of the 
plasma such as very often follows the transformation of the spermatid to 
spermatozoon. It begins with a considerable expansion of the plasma-vesicle 
(PI. XI, figs. 17-19), leading to the formation of a large sac of ectoplasm from 
