[Illustration: FIG. 30.—_Didymium difforme._ A, two sporangia (_spg_ 1 and 2) on a fragment of leaf (_l_); B, section of sporangium, with ruptured outer layer (_a_), and threads of capillitium (_cp_); C, a flagellula with contractile vacuole (_c.vac_) and nucleus (_nu_); D, the same after loss of flagellum; _b_, an ingested bacillus; E, an amoebula; F, conjugation of amoebulae to form a small plasmodium; G, a larger plasmodium accompanied by numerous amoebulae; _sp_, ingested spores. (After Lister.)] Again, in some cases the plasmodia themselves aggregate in the same way as the amoeboids do in the _Acrasieae_, and combine to form a compound fruit termed an "aethalium,"[98] with the regions of the separate plasmodia more or less clearly marked off. The species formerly termed _Aethalium septicum_ is now known as _Fuligo varians_. It is a large and conspicuous species, common on tan, and is a pest in the tanpits. Its aethalia may reach a {93}diameter of a foot and more, and a thickness of two inches. _Chondrioderma diffusum_, often utilised as a convenient "laboratory type," is common on the decaying haulms of beans in the late autumn. The interest of this group is entirely biological, save for the "flowers of tan."[99] {94}CHAPTER IV PROTOZOA (_CONTINUED_): SPOROZOA[100] II. Sporozoa. _Protozoa parasitic in Metazoa, usually intracellular for at least part of their cycle, rarely possessing pseudopodia, or flagella (save in the sperms), never cilia; reproduction by brood-formation, often of alternating types; syngamy leading up to resting spores in which minute sickle-germs are formed, or unknown (Myxosporidiaceae)._ This group, of which seven years ago no single species was known in its complete cycle, has recently become the subject of concentrated and successful study, owing to the fact that it has been recognised to contain the organisms which induce such scourges to animals as malarial fevers, and various destructive murrains. Our earliest accurate, if partial knowledge, was due to von Siebold, Kölliker, and van Beneden. Thirty years ago Ray Lankester in England commenced the study of species that dwell in the blood, destined to be of such moment for the well-being of man and the animals in his service; and since then our knowledge has increased by the labours of Manson, Ross and Minchin at home, Laveran, Blanchard, Thélohan, Léger, Cuénot, Mesnil, Aimé Schneider in France, Grassi in Italy, Schaudinn, Siedlecki, L. and R. Pfeiffer, Doflein in Central Europe, and many others.