1 12 Brebner. — On the Prothallus and Embryo of 
is that not infrequently the formation of the curved inter- 
secting vertical walls, even down to the last, may precede 
the horizontal wall, which cuts off the mother-cell of the 
sperm-cells (cf. Figs. 7, 9, and 10). All these figures 
were taken from antheridia developing on the prothallus, in 
which the mother-cells involved had already reached, or 
nearly reached, their adult condition before commencing to 
form the antheridia. In the case of the two latter figures, 
a developing antheridium of this type is represented, as seen 
from below (Fig. 9) and from above (Fig. 10). As far as the 
drawings permitted, corresponding walls have been lettered 
alike ; but to realize the point clearly it might be as well 
to make a tracing of Fig. 10, and then turn it over and super- 
pose it on Fig. 9, when the relation of the walls would at once 
become obvious. In Fig. 9 the two cells which will ulti- 
mately give rise to the spermatozoids are still quite young 
and merismatic, whereas in Fig. 10 the cover-cells have 
already reached their adult condition. This condition differs 
considerably from that represented by Prof. Campbell’s 
Figs. 8, 9, and 10 1 , where the growth of the antheridium as 
a whole goes on pari passu with that of the prothallus. As 
a result of the exceptional mode of development, in the most 
extreme case — and such was actually observed — there may 
be only a single vertical row of four spermatozoid-mother-cells 
visible in one plane, whereas in a normal case (e.g. Fig. 12) 
five vertical rows, each of four spermatozoid-mother-cells, 
may occur. Jonkman noted the fact that the number of 
spermatozoids formed in Angiopteris and Marattia was very 
variable, and gave as observed numbers 20-500 or even 
more 2 . — This exceptional state of matters in Danaea can 
only be looked upon as a further reduction due to late 
development. 
Archegonium. 
Material was not available for following the development 
of the archegonia, but the adult structure is essentially the 
Loc. cit. (a\ PI. T. 
1 
2 Loc. cit., p. 214. 
