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EXCRETED ELEMENTS. 6 1transparent, permitting a free view of their enclosed constructors, but in somefew, and notably in association with the genera Cothurnia, Vaginicola, andtheir allies, the loricae assume with age a deep chestnut hue, and are moreor less completely opaque. Certain of the representatives of the foregoinggroup are further distinguished by their possession of a supplementarysimple operculum or more complex valvular structure, which, upon thewithdrawal of the animalcule, closes the aperture of the lorica, and effectuallyprotects the animalcule from molestation from without. The greatestdiversity in form exhibited by the protective cases or loricae of the infusorialanimalcules isundoubtedly met with among the more simply organizedFlagellate section. Here we have several families, as, for example, theTrachelomonadidae, Dinobryonidae, and Salpingaecidae, notable for the diversityof contour exhibited by the domiciliary structures secreted those;appertaining to the one last named being particularly worthy of mention,as including forms which vie for elegance in outline with the classic vasesand amphorae of ancient Greece. Within this family, and also in that ofthe Dinobryonidae, more complex loricate types occur than among any asyet known Ciliata, many loricse in such instances remaining united to oneanother, and forming more or less extensive branching structures, highlysuggestive of the horny and chambered polyparies of the Sertularian zoophytesand Polyzoa ;for these last-named aggregations of ordinary simpleloricae the distinctive title of " zoothecia " has been adopted by the author.Although it mostly happens that the texture of the lorica is purely hornlikeor chitinous, it is sometimes found, as in Codonella, and among certainmembers of the genus Tintinmis, that a more or less considerable amountof sand-grains or other extraneous particles are incorporated within itssubstance. In a still more limited series of types, e. g. the genus Dictyocysta,sharing with Tintinnus a pelagic habitat, the shell or lorica ispurelysiliceous, variously perforate or fenestrate, and, in the absence of its characteristicoccupant, is scarcely to be distinguished from the elegantly latticedsiliceous shells of certain Polycystinae. As mentioned in the account givenof that family group, there are strong grounds for suspecting that theinvesting cuirass of certain pelagic Peridiniadae is likewise of a siliceousnature.The investing loricae of the Infusoria represent by no means the entireboth the Ciliata andsum of the structures produced by excretion.AmongFlagellata are found compound tree-like growths or " zoodendria," thatexhibit a highly complex type of organization. Reference is more especiallymade here to such an excreted compound pedicle as occurs in Anthophysavegetaus, a full account of the formation and mode of development of whichisplaced on record in connection with the account given of that species.In this particular typeit was shown by experiment that the ramifyingsupporting stalk is built up by excretion, from the posterior region of theassociated animalcules, of the residual particles of the substances first inceptedfor nutrient purposes mingled with some amount of cohesive mucus,