Page:Encyclopædia Britannica, Ninth Edition, v. 19.djvu/865

Rh MYCETOZOA.] PROTOZOA 841 spores (one corresponding to each nucleus of the enclosed plas- niodium) each of which has a cellulose coat, and (1) a capillitium of threads which hold the spores together. Each spore (chlamydo- spore) liberates on germination a single nucleated flagellula, which develops into an arnoebula, which in turn fuses with other amcebulaj to form the plasmodium. The Endosporea are essentially dwellers on rotten wood and such vegetable refuse. FIG. 111. Mycetozoa (after Do Davy). 1-G. Gi-rmination of spore (1) of Trichea raria, showing the emerging &quot;flattellula&quot; (4, 5), and its conversion into an &quot;ama bula&quot; (&amp;gt;&amp;gt;). 7 -IS. Series leading from spore to jilasmodiiim phase of Chondrioderma diffonne: 7, impure; 10, flagellula; V2, amoebula; 14, apposi tion of two amccbula! ; 15-17, fusions; 18, plasmodium. lit, 20. Spore-fruit (cyst) of J /iuxar/im Itucoplneum, Fr. (x 25), the former from the surface, the latter in section with the spores removed to show the sustentacular network or capillitium. 21. Section of the spore-cyst of Didymium squamuIosum, Vfith the spores removed to show the radiating capillitium # and the stalk. Sub-order 1. PERITIUCHKA, Zopf. Fam. 1. CLATHROPTYCHIACEJE, Rostafinski. Genera. Clathroptychium, Rost. ; Entcridium, Ehr. Fam. 2. CRIBRARIACE^E. Genera. Dictydiinn, Pers. ; Crilraria, Pers. Sub-order 2. ENDOTRICHEA, Zopf. Fam. 1. PUYSAREA. Genera. Physarum, Pers.; Cmtcrium, Trentcpol ; Badhamia, Berkeley ; Leocarpus, Link. ; Tilmadoche, Fr. j Fuligo (sEfhalium), Hall ; ^Ethaliopsis, Z. Fain. 2. DIHYMIACK./K. Genera. Didijinium; Lepidodcrma, De Bary. Fam. 3. SFUMARIACEJE. Genera. Spumaria, Pers. ; Diachca, Fries. Fam. 4. STKMONITICA. Genera. Stemonitis, Gleditsch ; Comatriclia, Preuss ; Lam- prodcrma, Rost. Fam. 5. ENERTHKNEMEA. Genera. Enerthemn, Bowman. Fam. 6. RETicuLARiACE.fi, Zopf. Genera. Amauroch&te, Rost.; Edicularia, Bull. Fain. 7. TRICHIXACE.-E. Genera. llcmiarojria, Rost. ; TricJiia, Hall. Fam. 8. ARCYUIACE/K. Genera. Arci/ria, Hall; Cornuvia, Rost.; Lycogala, Ehr. Fam. 9. PERICHJENACEJE. Genera. Perichsena, Fries. ; Lachnobolus, Fries. Fam. 10. LICEACE^E. Genera. Licca, Schrader ; Tubulina, Pers.; Lindbladia, Fries. ; Tululifem, Zopf. ORDER 3. EXOSPOREA, Zopf. Characters. The chlamydospore liberates an amoebula in the first instance, which develops into a flagellula. This subsequently returns to the amoeba form, and by fusion with other amcebulaj it forms a true fusion plasmodium. The spores are not produced within a cyst but upon the surface of column-like up-growths of the plasmodium, each spore (conidum) forming as a little spherical out growth attached to the column (conidioplior) by a distinct pedicle. Sole Genus. Ceratium. [This name must be changed, since it was already applied to a genus of .Dinoflagellata, when Famintzin and Woronin gave it to this Mycetozoon.] Further Remarks on Mycctozoa. About two hundred species of Mycetozoa have been described. Botanists, and especially those who occupy themselves with Fungi, have accumulated the very large mass of facts now known in reference to these organisms ; never theless the most eminent botanist who has done more than any other to advance our knowledge of Mycetozoa, namely, De Bary, has expressed the view that they are to be regarded rather as animals than as plants. The fact is that, once the question is raised, it becomes as reasonable to relegate all the Gymnoniyxa without exception to the vegetable kingdom as to do so with the Mycetozoa. Whatever course we take with the latter, we must take also with the Heliozoa, the Radiolaria, and the Keticularia. The formation of plasmodia, for which the Mycetozoa are conspicu ous, appears to be a particular instance of the general phenomenon of cell-conjugation. Small plasmodia are formed by some of the Proteomyxa ; but among the other Gymnoniyxa, excepting Myceto zoa, and among Corticate Protozoa, the fusion of two individuals (conjugation scnsu stricto) is more usual than the fusion of several. Zopf (13) has attempted to distinguish arbitrarily between conjuga tion and plasmodium formation by asserting that in the former the nuclei of the cells which fuse are also fused, whereas in the latter process the nuclei retain their independence. Both state ments are questionable. AYhat happens to the nucleus in such conjugations as those of the Gregarinae has not yet been made out, whilst it is only quite recently that Strasburger (30) has shown that the plasmodia of Mycetozoa contain numerous scattered nuclei, and it is not known that fusion does not occur between some of these. There is no doubt that the nuclei of plasmodia multiply by fission, though we have no detailed account of the process. The Sorophora are exceptional in that the ama-bfc which unite to form a cell-colony in their case do not actually fuse but only remain in close contact ; with this goes the fact that there are no large spore-cysts, but an identification of spore and spore-cyst. The anicebfe arrange themselves in stalked clusters (sori), and each be comes encysted : one may, in this case, consider the cyst equally as a spore or as a spore-cyst which produces but a single spore. The amoebai described by various writers as inhabiting the alimentary canal and the dung of higher animals (including man) belong to this group. The form described by Cunningham in the Quart. Jour. Micr. Sci., 1881, as Protomyxomyces coprinarius is appa rently related to the Copromyxa (Guttulina) protca of Fayod (31). The spore-fruits of the Endosporese occur in various degrees of elaboration. Usually they are (1) spherical or pear-shaped cysts with or without an obvious stalk (Fig. III. 19, 20, 21), and often have a brilliant colour, and are of a size readily observed by the naked eye, the plasmodia which give rise to them being by no means microscopic. But they may present themselves (2) as irregular ridges growing up from the plasmodium, when they are termed serpula forms. Lastly, the cysts may be united side by side in larger or smaller groups instead of forming at various sepa rate points of the plasmodium. These composite bodies are termed &quot;fruit-cakes 1 or &quot;aithalia,&quot; in view of the fact that the spore-cysts of Fuligo, also called /Ethalium the well-known &quot;flowers of tan&quot; form a cake of this description. The capillitium or network of threads which lies between the spores in the spore-cysts of Endosporese is a remarkable structure which exhibits special elaborations in detail in different genera, here i:&amp;lt;&amp;gt;t to be noticed for want of space. Although definite in form and structure, these threads are not built up by cells but are formed by a residual protoplasm (if. Sporozoa) which is left in the cyst after the spores have been segregated and enclosed each in its special coat. They are often impregnated by calcium carbonate, and exhibit crystalline masses of it, as does also the cyst-wall. The spores of the Mycetozoa are as a rule about the j-jVo th inch in diameter. They are produced by millions in the large fruit cakes of such forms as Fuligo. Often the spore-coat is coloured ; it always consists of a substance which gives the cellulose reaction with iodine and sulphuric acid. This has been sometimes con sidered an indication of the vegetable nature of the Mycetozoa, but cannot be so regarded since many animals (especially the Tunicata and various Protozoa) produce substances giving this same reaction. Dryness, low temperature, and want of nutriment lead to a dor mant condition of the protoplasm of the plasmodium of many Mycetozoa and to its enclosure in cyst-like growths known as &quot;sclerotia,&quot; which do not give rise to spores, but from which the protoplasm creeps forth unaltered when temperature, nutrition, and moisture are again favourable. The sclerotia are similar in nature to the hypnocysts of other Protozoa. The physiological properties chemical composition, digestive action, reaction to moisture, heat, light, and other physical influ ences of the. plasmodia of Mycetozoa have been made the subject of important investigations ; they furnish the largest masses of undifferentiated protoplasm available for such study. The reader is referred to Zopf s admirable treatise (13) as to these matters, and also for a detailed account of the genera and species. CLASS III. LOBOSA, Carpenter. Characters. Gymnoniyxa in which (as in the succeeding four classes) the amoeba-phase predominates over the others in perma nence, size attained, and physiological importance. The pseudo- XIX. 1 06