[Illustration: FIG. 53.--_A_, end of a branch from a male plant of _Madotheca_. The small side branchlets bear the antheridia, × 2. _B_, two young antheridia (_an._), the upper one seen in optical section, the lower one from without, × 150. _C_, a ripe antheridium, optical section, × 50. _D_, sperm cells with young spermatozoids. _E_, ripe spermatozoids, × 600.] When ripe, if brought into water, the antheridium bursts at the top into a number of irregular lobes that curl back and allow the mass of sperm cells to escape. The spermatozoids, which are derived principally from the nucleus of the sperm cells (53, _D_) are so small as to make a satisfactory examination possible only with very powerful lenses. The ripe spermatozoid is coiled in a flat spiral (53, _E_), and has two excessively delicate cilia, visible only under the most favorable circumstances. The female organ in the bryophytes is called an "archegonium," and differs considerably from anything we have yet studied, but recalls somewhat the structure of the oögonium of _Chara_. They are found in groups, contained in little bud-like branches (54, _H_). In order to study them, a plant should be chosen that has numbers of such buds, and the smallest that can be found should be used. Those containing the young archegonia are very small; but after one has been fertilized, the leaves enclosing it grow much larger, and the bud becomes quite conspicuous, being surrounded by two or three comparatively large leaves. By dissecting the young buds, archegonia in all stages of growth may be found. [Illustration: FIG. 54.--_A-D_, development of the archegonium of _Madotheca_. _B_, surface view, the others in optical section. _o_, egg cell, × 150. _E_, base of a fertilized archegonium, containing a young embryo (_em._), × 150. _F_, margin of one of the leaves surrounding the archegonia. _G_, young sporogonium still surrounded by the much enlarged base of the archegonium. _h_, neck of the archegonium. _ar._ abortive archegonia, × 12. _H_, short branch containing the young sporogonium, × 4.]