12 
H. MARSHALL WARD. 
or more archegoiiia. We may take that of Marsilea as a 
type. The diagram (Fig. 2) represents a section through 
the germinating macrospore, with its only partially exposed 
prothallus, bearing an archegonium which differs from that 
of the Fern in several points. 
Fig. 2. — Diagram of partially free $ protballium of Marsilea, it is re- 
duced to little more than the archegonium, which hardly projects from 
the surface, and has very few neck cells. The “ canal-cell,” however, 
appears. The space ( X ) becomes filled with fluid. 
In the first place, its neck, instead of being a long, freely 
projecting structure of several tiers of cells, hardly pro- 
trudes at all, and is formed of two tiers of four cells each ; 
in plan these cells are arranged crosswise, and are almost 
flush with the general level of the prothallium. Between 
them, however, the young oosphere allows part of its sub- 
stance, cut off as before, to penetrate as the canal cell.” 
Besides a separation of the sexes, then, we have in Rhi- 
zocarps a much smaller prothallus which never becomes 
entirely free ; and as the prothallus tends to be withdrawn 
(as it were) into the spore, so, too, the archegonia, &c., 
appear to be held back in the prothallus, and the neck to be 
a less protruded structure. For a third stage in this re- 
markable process we may select Selaginella. Here the 
macrospores and microspores are not only produced in dif- 
ferent sporangia, but the macro- and micro-sporangia are 
borne on different leaves ; the sexes are further separated. 
As before, the microspore undergoes the less extensive 
development ; its contents becomes divided up into a few 
cells, the majority of which produce antherozoids. The 
spore then bursts and sets them free ; the process may be 
considered as the formation of a rudimentary internal pro- 
thallus reduced to little more than the antherozoid mother- 
cells (antheridium). In the macrospore, a small prothallus 
forms internally, and is just allowed to peep forth and 
