434 Wilson. — Spermatogenesis in the Bryophyta . 
The cytoplasm is rather denser than that of Mnium , but, as in that plant, 
its structure is very regular ; neither deeply staining granules nor vacuoles 
are found in the cells. The various stages of division have not been studied 
in great detail in this species, but as far as they have been observed they 
closely resemble those already described in Mnium. One point of difference 
has, however, been observed. In A trichum undulatum division of the 
nucleolus has been discovered in spermatogenic cells forming part of young 
antheridia (Fig. 45), and it seems probable that in this case the separation 
of a body from the nucleolus takes place prior to all the divisions of the 
spermatogenic cells. As in Mnium , no trace of centrosomes has been 
discovered at any stage in the divisions. 
On account of the statements made by J. and W. Docters van Leeuwen- 
Reijnvaan (41, 42) the final division of the spermatogenic cells was carefully 
investigated. As in Mnium hommn , this mitosis closely resembles the 
previous ones, and in consequence the same methods were here employed to 
determine the comparative ages of the antheridia. Although the results 
obtained were not so constant as those given by the former species, the final 
mitosis could still be recognized with considerable certainty. In the meta- 
phase of this division the spindle is not well marked, and no centrosomes are 
present. Its orientation is variable, for while in some cases its long axis coin- 
cides with that of the cell (PI. XXXVIII, Fig. 48), in others it is diagonally 
arranged (PI. XXXVII, Fig. 46). The number of chromosomes is con- 
siderably greater than that found in Mnium. As the result of several 
countings made in polar views of the metaphase, it has been concluded that 
seventeen chromosomes are present, although in a few cases only sixteen 
could be distinguished (Fig. 47). Separation of the daughter chromosomes 
goes on in the usual manner, and during the anaphase the number could 
be again determined in polar views ; as before, seventeen chromosomes are 
found (PL XXXVIII, Fig. 49). It is therefore obvious that no reduction 
has taken place. The telophase is normal, and a wall is formed between 
the resulting cells in the usual manner. 
Shortly after the final division is completed shrinkage takes place, and 
each cell becomes free from its investing walls. The spermatids so pro- 
duced are approximately spherical in form. Each possesses a large nucleus 
which contains a deeply staining nucleolus. The cytoplasm is regularly 
alveolar in structure and contains no deeply staining granules (Fig. 50). 
A protrusion is now produced on the nucleolus, and soon a small spherical 
body is cut off by constriction, which at first remains in contact with it. 
Shortly afterwards this body migrates into the cytoplasm and passes 
towards the cell membrane (Fig. 51), finally coming to rest on the periphery 
(Fig. 52). Later on this functions as the blepharoplast. 
The nucleolus meanwhile continues to bud (Figs. 51-3) and produces 
two more small bodies which do not at once separate. In consequence, 
