ria_, _Diachaea_, _Dictydium_, &c. In _Spumaria_,
_Reticularia_, _Lycogala_, &c., they are almost obsolete.[X] In no
group is the examination of the development of structure more
difficult, for the reasons already alleged, than in the Myxogastres.

[Illustration: FIG. 12.--_Diachaea elegans._]

[Illustration: FIG. 13.--_Cyathus vernicosus._]

NIDULARIACEI.--This small group departs in some important particulars
from the general type of structure present in the rest of the
Gasteromycetes.[Y] The plants here included may be described under
three parts, the mycelium, the peridium, and the sporangia. The
mycelium is often plentiful, stout, rigid, interlacing, and coloured,
running over the surface of the soil, or amongst the vegetable debris
on which the fungi establish themselves. The peridia are seated upon
this mycelium, and in most instances are at length open above, taking
the form of cups, or beakers. These organs consist of three strata of
tissue varying in structure, the external being fibrous, and sometimes
hairy, the interior cellular and delicate, the intermediate thick and
at length tough, coriaceous, and resistant. When first formed, the
peridia are spherical, they then elongate and expand, the mouth being
for some time closed by a veil, or diaphragm, which ultimately
disappears. Within the cups lentil-shaped bodies are attached to the
base and sides by elastic cords. These are the sporangia. Each of
these has a complicated structure; externally there is a filamentous
tunic, composed of interlaced fibres, sometimes called the peridiole;
beneath this is the cortex, of compact homogenous structure, then
follows a cellular thicker stratum, bearing, towards the centre of the
sporangia, delicate branched threads, or sporophores, on which, at
their extremities, the ovate spores are generated, sometimes in pairs,
but normally, it would seem that they are quaternary on spicules, the
threads being true basidia. The whole structure is exceedingly
interesting and peculiar, and may be studied in detail in Tulasne's
memoir on this group.

SPHAERONEMEI.--In this very large and, within certain limits, variable
order, there is but little of interest as regards structure, which is
not better illustrated elsewhere; as, for instance, some sort of
perithecium is always present, but this can be better studied in the
_Sphaeriacei_. The spores are mostly very minute, borne on delicate
sporophores, which originate from the inner s