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NUCLEUS OR ENDOPLAST. 73to indicate the more important function in the economyof the infusorialbody that it may be predicated to fulfil. Beyond doubt, the leadingfunction of the contractile vesicular system is excretory, in the gettingrid of the comparatively vast amount of fluid constantly brought intothe body through the ciliary or other currents in combination with theincepted food-material. As isconspicuously evident when watching thefeeding process in a Vorticella or other highly organized Infusorium, eachspheroidal pellet or isolated fragment of incepted pabulum, regurgitatedthrough the yielding endoplasm, is enclosed within an equal or evenmore extensive mass of water, and which liquid, without some specialoutlet for its discharge, would soon accumulate to an extent incompatiblewith the well-being of the animalcule. In this relation, the contractilevesicle with its tributary canaliculi and lacunae, clearly visible in certaininstances and doubtless existing in all, enacts the part of a highly elaborateand efficient drainage system, collecting the superabundant fluidfrom every part of the body-plasma, and discharging it after its receptioninto the single or several more or less spheroidal,reservoir-like centresbeyond the cuticular periphery. That the considerable quantity of waterthus brought constantly into intimate contact with the body-plasma, and asit were circulated throughout every portion of its substance, plays animportant rdle in the reoxygenization of its molecular constituents, and thusfulfilsa rudimentary respiratory function, may be likewise consistently premised,as also that by the time this same water has circulated through theanimalcule's tissues, and has debouched into the reservoir or contractilevesicle from which it is eventually discharged, its chemical composition hasbecome materially altered through both the loss of oxygen and the incrementof carbonic acid and other waste material. It is possible that the palepink hue, mostly prevalent in the contents of the expanded vesicle, owes itspresence to such chemical reaction, and itpresents at any rate a pointworthy of future investigation.Vacuolar spaces possessing no rhythmically pulsating properties, sometimesconstant in position, at others sharing in the movements of the parenchyma,and not unfrequently exhibiting slowly contractile motions whichterminate in their permanent obliteration, are constantly met with amongthe Infusoria. In some few instances this vacuolation, as more fully relatedat page 58, is developed to such an extent that the entire endoplasmicsubstance presents a mere trabecular or network-like appearance. Thisextreme type is especially prominent in the Flagellate group of the Noctilucidae,and attains a closely parallel degree of developmentin the Ciliateforms TracJielius ovum and Loxodes rostrum.Nucleus or Endoplast, and Nucleolus or Endoplastule.These important organs, while possessing a stronger claim for consideration,perhaps, in that section specially devoted to the description ofthe reproductive structures and phenomena, represent in themselves such