The laws and mechanics of circulation, with the principle involved in animal movement . g the walls of the little animal (B), the one constitutingthe internal layer, or entoderm (i), the other the skin-layer, orexoderm (e); while the fluids flow in and out of the littlestomachal cavity thus formed through the oral orifice (o) dur-ing the rhythmical expansions and contractions taking placein it. Flowing in, of course, during expansion and the devel- 56 ACTION IN GASTRULA. opment of low pressure which this produces till pressure isuniform, and flowing out again by reflux action through theroute
The laws and mechanics of circulation, with the principle involved in animal movement . g the walls of the little animal (B), the one constitutingthe internal layer, or entoderm (i), the other the skin-layer, orexoderm (e); while the fluids flow in and out of the littlestomachal cavity thus formed through the oral orifice (o) dur-ing the rhythmical expansions and contractions taking placein it. Flowing in, of course, during expansion and the devel- 56 ACTION IN GASTRULA. opment of low pressure which this produces till pressure isuniform, and flowing out again by reflux action through theroute of ingress during contraction and the development ofhigh pressure which this produces to equalize pressure ; in thismanner readily producing afflux and efflux of the fluids in thestomachal cavity : while the changes of form which this in-volves in the individual cells, in order to produce these actionsshould increase circulation in them correspondingly, and whichthe scheme calls for in order to generate the force which isexpended in these actions, the one involving the other. .Allof. Fig. 12— Gastrula of a Chalk-sponge (Olynthus). A, from the outside ; B, in longi-tudinal section through the axis; g, primitive intestine ; o, primitive mouth ; i,intestinal-layer, or entoderm ; e, skin-layer, or exoderm.—Haeckel. which is plain enough. But the circumstance in whichinterest culminates is the one of coordination in the cell-colony,so as to compel the two layers to expand and contractsimultaneously, in order to swallow the food and effect thepumping action for producing afflux and efflux of the fluids inthe primitive intestine (g); otherwise impossible. In short, theinner layer (/) or intestine expands and contracts snychronouslywith the outer wall or skin-layer (e), which answers to themuscular envelope in the body-walls in the more advancedstages in development, the two acting in harmonious concertto this end, as is the case in the later stages ; only there is nonervous appara
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