. Cassell's natural history. Animals; Animal behavior. THE XVCLEUS OR EXDOI-LAST IX THE IXFUisOJilA. fcy a definite circle of endoplasm, but has rays, or tubular passages, tapering outwards around it {Fig. 2, cv). The passages are numerous, and may be seen to ramify at their extreme ends, and they are weak spots in the cortical layer over the more fluid endoplasm, extending far and wide from the vesicle. These passages transmit light more readily than the protoplasm in which they are placed, <md it therefore occurs that, as water tills them, and they increase in diameter and length, they ar
. Cassell's natural history. Animals; Animal behavior. THE XVCLEUS OR EXDOI-LAST IX THE IXFUisOJilA. fcy a definite circle of endoplasm, but has rays, or tubular passages, tapering outwards around it {Fig. 2, cv). The passages are numerous, and may be seen to ramify at their extreme ends, and they are weak spots in the cortical layer over the more fluid endoplasm, extending far and wide from the vesicle. These passages transmit light more readily than the protoplasm in which they are placed, <md it therefore occurs that, as water tills them, and they increase in diameter and length, they are nearly as light-transmitting as the main space with which they are continuous. They become largest JTist before the conti-action of the vesicle, and they sometimes do not disappear until after its contraction. It is evident that the watery contents of the passages are pressed upon by the con- ti-action of the surrounding protoplasm, and that this water and that of the space penetrate, during contraction, into tliis environing substance. Movement may be noticed under the outer tissue, here and there, within and along the lines of the passages. More or less defined com- munications exist between the outside water and the contractile vesicles through the ectoplasm, and the vesicle receives pure water from without, and collects and expels the impure water from within the animal. It is evident that the function of the contractile vesicle is of great importance to the animal, and it may relate to the elimination or removal of certain soluble mattere resembling the urinary secretions. It may also relate to an internal circulation of water. The rhythm of the dilatation and contraction is very remarkable, and Saville Kent states that " the time occupied between the consecutive pulsations of this organ is found, â under normal conditions, to present a constant average among individuals of the same species, varying from a few seconds only in certain forms, to over sixty or even on
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