EXCRETED ELEMENTS. 6 1 



transparent, permitting a free view of their enclosed constructors, but in some 

 few, and notably in association with the genera Cothurnia, Vaginicola, and 

 their allies, the loricae assume with age a deep chestnut hue, and are more 

 or less completely opaque. Certain of the representatives of the foregoing 

 group are further distinguished by their possession of a supplementary 

 simple operculum or more complex valvular structure, which, upon the 

 withdrawal of the animalcule, closes the aperture of the lorica, and effec- 

 tually protects the animalcule from molestation from without. The greatest 

 diversity in form exhibited by the protective cases or loricae of the infuso- 

 rial animalcules is undoubtedly met with among the more simply organized 

 Flagellate section. Here we have several families, as, for example, the 

 Trachelomonadidae, Dinobryonidae, and Salpingaecidae, notable for the diver- 

 sity of 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 vases 

 and amphorae of ancient Greece. Within this family, and also in that of 

 the Dinobryonidae, more complex loricate types occur than among any as 

 yet known Ciliata, many loricse in such instances remaining united to one 

 another, and forming more or less extensive branching structures, highly 

 suggestive of the horny and chambered polyparies of the Sertularian zoo- 

 phytes and Polyzoa ; for these last-named aggregations of ordinary simple 

 loricae the distinctive title of " zoothecia " has been adopted by the author. 

 Although it mostly happens that the texture of the lorica is purely horn- 

 like or chitinous, it is sometimes found, as in Codonella, and among certain 

 members of the genus Tintinmis, that a more or less considerable amount 

 of sand-grains or other extraneous particles are incorporated within its 

 substance. In a still more limited series of types, e. g. the genus Dictyo- 

 cysta, sharing with Tintinnus a pelagic habitat, the shell or lorica is purely 

 siliceous, variously perforate or fenestrate, and, in the absence of its charac- 

 teristic occupant, is scarcely to be distinguished from the elegantly latticed 

 siliceous shells of certain Polycystinae. As mentioned in the account given 

 of that family group, there are strong grounds for suspecting that the 

 investing cuirass of certain pelagic Peridiniadae is likewise of a siliceous 

 nature. 



The investing loricae of the Infusoria represent by no means the entire 

 sum of the structures produced by excretion. Among both the Ciliata and 

 Flagellata are found compound tree-like growths or " zoodendria," that 

 exhibit a highly complex type of organization. Reference is more especially 

 made here to such an excreted compound pedicle as occurs in Anthophysa 

 vegetaus, a full account of the formation and mode of development of which 

 is placed on record in connection with the account given of that species. 

 In this particular type it was shown by experiment that the ramifying 

 supporting stalk is built up by excretion, from the posterior region of the 

 associated animalcules, of the residual particles of the substances first in- 

 cepted for nutrient purposes mingled with some amount of cohesive mucus, 



