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1 92 NATURE AND AFFINITIES OF THE SPONGES.existence a simply flagellate structural type. In their most characteristicform, these reproductive bodies or cell-aggregatesconsist of a uniformseries of collared zooids, but by irregular growth one half may arriveat or pass maturity in advance of the other, the product then being acompound structurepresenting a close correspondence with that phase ofdevelopment of the Metazoic ovum known as the amphiblastula. Since,however, these bodies are in no way comparable with the Metazoic ovumnot being the product of the concourse of true sexual elements the aboveas itlikeness issimply homoplastic, and the body as a whole, consistingdoes of an aggregation of numerous independent zooids, may be mostappropriately denominated a " swarm-gemmule." While no direct approachto the production of a similar compound gemmule occurs among thetypical Infusoria-Flagellata, as at present known, something much akinto it obtains in the protophytic type Volvox globator, which liberatesfrom its interior, free-swimming gemmules that take the form of sphericalaggregations of biflagellate daughter-cells. In their isolated state, on theother hand, the svvarm-gemmules of the sponge-stock are directly comparablewith the free-swimming subspheroidal colony-stock of the flagellateInfusoria Synura, Syncrypta, and Uroglena, or with the attached subspheroidalclusters of Codosiga and Anthophysa.In certain respects, as already pointed out at page 41 et seq., a veryremarkable and suggestive analogy in the direction of the Spongida isfurnished by the Protozoic group of the Myxomycetes or Mycetozoa.Here we find the essential elements consisting primarily of independentflagellate zooids possessing a spheroidal endoplast, contractile vesicles,taking in solid nutriment, and presenting other characters in common withthe ordinary Flagellata. Passing their matured flagellate condition thesenow assume an amoebiform condition and coalescing in large numbers, as inthe case of the Spongozoa, form a colossalamcebiform mass, the plasmodium,not unlike the cytoblastema of a sponge with its amcebiform contents,out of which by a species of encystment the characteristic fungus-likesporangia are developed. These sporangia are to a considerable extentcomparable with the hibernating encystments or so-called " gemmules "of Spongilla and other sponges, and subsequently, through the processof segmentation, become resolved into innumerable minute spores, whichagain give birth to a host of flagellate monadiform zooids resembling thosefrom whence they originally sprang. It is further remarkable and suggestiveof some distant affinity with the Spongida, that the network of fineinterlacing threads, or " capillitium," that frequently binds the enclosedspores together, closely corresponds with the fine horny fibre of thekeratose sponge-series ;while in the substance of the outer wall or ' peridium" of the sporangia of some Mycetozoa, such as Didymium nigripes andD. serpula (see PI. X. Figs. 30 and 31), calcareous deposits resemblingsponge spicula are developed.It is clearly manifest that in a very singular manner, and to a marked