7 o 
THE TASMANIAN NATURALIST 
bricks, flower-pots, wet tree-fern stumps, and such like place. You must 
not be too hasty in finding prothallia ; for all conservatories are infested 
with a flat, pale green liverwort, Lunularia, which may be mistaken for 
them. In Lunularia the substance is not very thin, is pale green, and 
dotted with minute white spots ; prothallia are very delicate, and darker 
When a prothallium has reached sufficient age it develops on the under 
surface the essential organs of reproduction, the antheridia and 
archegonia. 
The archegonia should be understood, as we shall require to refer 
to them again. An archegonium is a flask-shaped thing containing a 
single little body destined to become an egg. In prothallia of ferns 
the archegonia are sunk in its substance. When one of the eggs 
has become fertilised all further development of the prothallium ceases, 
and the whole available energy is turned to develop the embryo. This 
embryo now grows into a fern like the one from which the spore was 
shed. This alternation of fern and prothallium always continues, and is 
commonly spoken of as the alternation of generation The fern only 
bears spores, and is the spore-bearing generation or sporophyte ; the 
prothallium only bears sexual organs, and is the sexual generation or 
gametophyte. These names also it is desirable to remember for future use. 
Here we have a rough life-history. Not only do ferns bear many 
sporangia on large leaves, but they live two independent existences, of 
which the sporophyte is the more important. In dealing with other 
groups of plants we shall meet with the same details only under various 
modilications. The sporangium is an organ old as the hills, and far 
older. It appeared first in almost the most primitive of plants — to run 
through the whole series of groups, even to the modern flowering plants. 
However it may be modified and thrust about to different parts of a 
plant, it is always truly the same. Archegonia are not of so ancient a 
lineage, and do not extend to the highest group, but they first appear in 
a primitive condition in some alga;, extend through mosses, ferns, 
lycopods to conifers, after which they vanish. 
The alternation of generations is also far-reaching, L appears at 
least in the red sea-weeds, and may be traced right through the other 
groups to the flowering plants Further details will be enlarged upon 
when we discuss other groups. 
Hn elementary Review of JBarine invertebrate 
Hnimals 
(For Young Students) 
By T. THOMPSON FLYNN, B.Sc. 
T; IVING things as a whole are grouped into one or other of two 
great kingdoms ; one including animals, the other, plants. As we 
see them in the higher forms, these are easily distinguished from one 
