The Myxosporidiaceae (Fig. 36) are parasitic in various cold-blooded animals. They are at least binucleate in the youngest free state, and become large and multinucleate apocytes, which may bud off outgrowths as well as reproduce by spores. The spores of the apocyte are not produced by simultaneous breaking up, but by successive differentiation. A single nucleus aggregates around itself a limited portion of the cytoplasm, and this again forms a membrane, becoming an archespore or a "pansporoblast," destined to produce two spores; within this, nuclear division takes place so as to form about eight nuclei, two of which are extruded as abortive, and of the other six, three are used up in the formation of each of the two spores. Of these three nuclei in each spore, two form nematocysts, like those of a Coelenterate (p. [246] f.), at the expense of the surrounding plasm; while the third nucleus divides to form the two final nuclei of the reproductive body. The whole aggregate of the reproductive body and the two nematocysts is enveloped in a bivalve shell. In what we may call germination, the nematocysts eject a thread that serves for attachment, the valves of the shell open, and the binucleate mass crawls out and grows afresh. Nosema bombycis Nägeli (the spore of which has a single nematocyst) is the organism of the "Pébrine" of the silkworm, which was estimated to have caused a total loss in France of some £40,000,000 before Pasteur investigated the malady and prescribed the effectual cure, or rather precaution against its spread. This consisted in crushing each mother in water after it had laid its eggs and seeking for pébrine germs. If the mother proved to be infected, her eggs were destroyed, as the eggs she had laid were certain to be also tainted. Balbiani completed the study of the organism from a morphological standpoint. Some Myxosporidiaceae produce destructive epidemics in fish.
Fig. 36.—A, Myxidium lieberkühnii, amoeboid phase; B, Myxobolus mülleri, spore with discharged nematocysts (ntc); C, spores (psorosperms) of a Myxosporidian. ntc, nematocysts. (From Parker and Haswell.)
The Dolichosporidia or Sarcosporidiaceae are, in the adult state, elongated sacs, often found in the substance of the voluntary muscles, and known as "Rainey's" or "Miescher's Tubes"; they are at first uninucleate, then multinucleate, and then break up successively into uninucleate cells, the spores, in each of which, by division, are formed the sickle-shaped zoospores.[[114]]
CHAPTER V
PROTOZOA (CONTINUED): FLAGELLATA
III. Flagellata.
Protozoa moving (and feeding in holozoic forms) by long flagella: pseudopodia when developed usually transitory: nucleus single or if multiple not biform: reproduction occurring in the active state and usually by longitudinal fission, sometimes alternating with brood-formation in the cyst or more rarely in the active state: form usually definite: a firm pellicle or distinct cell-wall often present.
The Flagellates thus defined correspond to Bütschli's group of the Mastigophora. The lowest and simplest forms, often loosely called "Monads," are only distinguishable from Sarcodina (especially Proteomyxa) and Sporozoa by the above characters: their artificial nature is obvious when we remember that many of the Sarcodina have a flagellate stage, and that the sperms of bisexual Sporozoa are flagellate (as are indeed those of all Metazoa except Nematodes and most Crustacea). Even as thus limited the group is of enormous extent, and passes into the Chytridieae and Phycomycetes Zoosporeae on the one hand, and by its holophytic colonial members into the Algae, on the other.[[115]]
Classification.