NUCLEUS OR ENDOPLAST. 73 



to indicate the more important function in the economy of the infusorial 

 body that it may be predicated to fulfil. Beyond doubt, the leading 

 function of the contractile vesicular system is excretory, in the getting 

 rid of the comparatively vast amount of fluid constantly brought into 

 the body through the ciliary or other currents in combination with the 

 incepted food-material. As is conspicuously evident when watching the 

 feeding process in a Vorticella or other highly organized Infusorium, each 

 spheroidal pellet or isolated fragment of incepted pabulum, regurgitated 

 through the yielding endoplasm, is enclosed within an equal or even 

 more extensive mass of water, and which liquid, without some special 

 outlet for its discharge, would soon accumulate to an extent incompatible 

 with the well-being of the animalcule. In this relation, the contractile 

 vesicle with its tributary canaliculi and lacunae, clearly visible in certain 

 instances and doubtless existing in all, enacts the part of a highly ela- 

 borate and efficient drainage system, collecting the superabundant fluid 

 from every part of the body-plasma, and discharging it after its reception 

 into the single or several more or less spheroidal, reservoir-like centres 

 beyond the cuticular periphery. That the considerable quantity of water 

 thus brought constantly into intimate contact with the body-plasma, and as 

 it were circulated throughout every portion of its substance, plays an 

 important rdle in the reoxygenization of its molecular constituents, and thus 

 fulfils a rudimentary respiratory function, may be likewise consistently pre- 

 mised, as also that by the time this same water has circulated through the 

 animalcule's tissues, and has debouched into the reservoir or contractile 

 vesicle from which it is eventually discharged, its chemical composition has 

 become materially altered through both the loss of oxygen and the incre- 

 ment of carbonic acid and other waste material. It is possible that the pale 

 pink hue, mostly prevalent in the contents of the expanded vesicle, owes its 

 presence to such chemical reaction, and it presents at any rate a point 

 worthy of future investigation. 



Vacuolar spaces possessing no rhythmically pulsating properties, some- 

 times constant in position, at others sharing in the movements of the paren- 

 chyma, and not unfrequently exhibiting slowly contractile motions which 

 terminate in their permanent obliteration, are constantly met with among 

 the Infusoria. In some few instances this vacuolation, as more fully related 

 at page 58, is developed to such an extent that the entire endoplasmic 

 substance presents a mere trabecular or network-like appearance. This 

 extreme type is especially prominent in the Flagellate group of the Nocti- 

 lucidae, and attains a closely parallel degree of development in the Ciliate 

 forms TracJielius ovum and Loxodes rostrum. 



Nucleus or Endoplast, and Nucleolus or Endoplastule. 



These important organs, while possessing a stronger claim for consi- 

 deration, perhaps, in that section specially devoted to the description of 

 the reproductive structures and phenomena, represent in themselves such 



