REPRODUCTIVE ORGANS OF HEPATICACEA. 375 
in the different genera of Mosses. The operculum, as already 
stated, is formed by a projection of the outer layer of the wall 
of the sporangium. At the point where the operculum separates 
an elastic ring or annulus is produced, which encircles the mouth 
of the sporangium. 
In germination, the inner coat of the spore is protruded as 
a tubular process, which ultimately produces a kind of pro- 
thallium in the form of a green cellular branched mass, some- 
what like a Conferva. This is called the Protonema, and upon 
its threads are subsequently developed leafy shoots, upon which 
archegonia and antheridia are afterwards developed. In Mosses, 
therefore, we have another instance of alternation of generations. 
7. Hepaticace& or Liverworts.—The reproductive organs 
of Liverworts are of two kinds like those of Mosses, to which 
this order is closely allied; they are called antheridia, and 
Fie. 830. Fie. 831. 
WW 
Fig. 830. A portion of the thallus or thalloid stem of Marehantia polymorpha. 
7. Receptacle, supported on a stalk, s. In the upper surface of the recep- 
tacle the antheridia are imbedded.— Fig. 831. Antheridium of Mar- 
chantia, discharging its small cellular contents (sperm-cells). 
archegonia or pistillidia, and both kinds may be found on the 
same plant, or on different plants; hence these plants are 
either monecious or diwcious. 
The antheridia or male organs are variously situated in the 
different genera of this order ; thus, in the leafy plants they are 
placed in the axils of leaves, as in some species of Jungermannia ; 
in other plants they occur in the substance of the frond or thal- 
loid expansion, as in ficcia and Fimbriaria ; and in others, as 
in Marchantia, they are found imbedded in the upper surface 
of peltate or discoid-stalked receptacles (fig. 830, 7). The an- 
theridia are small, generally shortly stalked, cellular sacs, of an 
oval (fig. 831) or somewhat flask-shaped form, in which are 
