Wilson.-—- Spermatogenesis in the Bryophyta . 447 
it is again absent, but appears in the penultimate and final divisions in that 
organ. It is interesting to note that the stages at which this body is pro- 
duced in Mnium hornum agree closely with those at which centrospheres 
and centrosomes have been described in several Liverworts. These latter 
structures, if present at all, are generally discovered at the meiosis and 
during the divisions of the spermatogenic cells. It may therefore be sug- 
gested that in the case of Mnium hornum the production of a body from 
the nucleolus during certain periods represents a late stage of reduction in 
centrosome formation. 
It may be supposed that at an early period in its phylogenetic history 
Mnium possessed centrosomes of nuclear origin similar to those described 
in Mar chan tia by Ikeno. During the specialization that is generally 
admitted to have taken place in the Musci these have become functionless, 
and in consequence have almost disappeared, being represented at the 
present time only by the bodies cut off from the nucleolus prior to certain 
divisions. 
If this supposition is admitted the direct formation of the blepharo- 
plast from the nucleus in the Musci can be more easily correlated with its 
centrosomic origin in Marchantia and other Hepatics. In Marchantia the 
centrosome derived from the nucleus just before the final division persists 
in the daughter-cells, and functions as the blepharoplast in the spermatids. 
In Mnium , the body produced at the final division (phylogenetically the 
centrosome) having no function soon disappears. In the spermatid a similar 
body arises from the nucleus, and now, having taken on an additional func- 
tion, persists as the blepharoplast. The formation of bodies from the 
nucleolus in the cells in the vicinity of the stem apex has already been 
mentioned. In these cases, as pointed out, this production of bodies is not 
associated with cell-division, and the mass separated is not regarded as 
possessing any phylogenetic relation to the centrosome. A similar produc- 
tion of bodies from the nucleoli of resting cells has been described in several 
animals and plants by Walker and Tozer (71). 
It is possible that the nuclear origin of the blepharoplast is more wide- 
spread than is generally supposed. In several cases where this body is 
described as arising de novo in the cytoplasm and in the vicinity of the 
nucleus, it is conceivable that it really originates from the latter structure. 
The plasmoderm origin of the blepharoplast described by Mottier in 
Char a is of interest in connexion with the similarity which, as long ago as 
1892, was pointed out by Strasburger (61) to exist between the spermato- 
genesis of this plant and that of the Musci. The spermatid of A trichum 
shown in Fig. 56, PI. XXXVIII, bears a considerable resemblance to the 
drawing of the spermatid of Chara given by Mottier (47) in his Fig. 1, 
although in the former case the blepharoplast is of nuclear, while in the latter 
it is of plasmodermic origin. The results obtained by a re-examination of 
