Respiration in Invertebrate Animals. 247 



albuminous compound. It possesses higlier organic properties in 

 those orders in which the tentacles are closed, than in those in 

 which they are open. In the former it sojourns longer in the 

 visceral cavdty under the influence of the Zoochemical forces. 

 It is in the interior of the cells of the solid structures that the 

 chylaqueous fluid acquires its final properties. It suflFers here 

 a second and higher nutritive and respiratory change, or derives 

 from the chylaqueous mass, still in the visceral cavity, a further 

 supply of oxygen. The chylaqueous fluid is aerated in two modes ; 

 1st, every portion of the element from without, which is admitted 

 into the splanchnic cavity, brings with it a fresh supply of highly 

 oxygenized air ; and 2nd, it exchanges its carbonic acid for the 

 oxygen of the surrounding element, in accordance with the prin- 

 ciples of ordinary aquatic breathing. It is therefore a reservoir of 

 richly oxygenated fluid, fitted well to impart a renewed proportion 

 of oxygen to the moi-e highly vitalized contents of the cells. It 

 is evident that it is only by a clear statement of these apparently 

 irrelevant particulars, that the anatomist can arm the phy- 

 siologist with an adequate conception of the physical conditions, 

 under which the respiratory function occurs in these degraded 

 organisms. In all actiniform polypes, the bottom of the stomach 

 sommunicates, by means of a sphincteric aperture, with the peri- 

 gastric chambers. It is by this route that the large mass of the 

 contents of these latter cavities are derived from without. The 

 contained fluid receives the fii'st impress of the vital chemistry, in 

 its passage over the gastric surfaces. It is then prepared to un- 

 dergo the respiratory changes in the visceral cavities. The pre- 

 ceding observations apply to the third (fig. 1) variety of plan (ex- 

 emplified in the Asteroid families), on which in zoophytes the 

 fluids are elaborated. There is little difi^erence of structure be- 

 tween the asteroid and helianthoid polypes. In the former the 

 stomach is prolonged into the axis of the polypidom (c). The 

 perigastric chambers [d) also communicate, but in a less direct 



one fact of singular interest should be remembered, the truth of which the 

 author has estabhshed by numerous observations. The cells of the solid 

 tissues are contractile ; they contract and dilate : in the Cephalopods, the 

 pigmented cells of the integumentary structures exhibit this property with 

 remarkable distinctness. The pigment is deposited in the substance of the 

 cell-wall. When the cell contracts the coloiu-ed point disappears, when it 

 expands it assumes a conspicuous area. This is the simple explanation of 

 the singular power, with which the Cephalopods are gifted, of changing their 

 colour. It appUes also to the chameleon. But in invertebrate animals it 

 is not confined to the pigmented cells. It is exhibited by the non-pig- 

 mented cells of neaily all the structures of the body. The author has ven- 

 tured in this place to bring it under the attention of the physiologist, be- 

 cause it is unquestionably a property of great importance in the cuculation 

 and aeration of the fluids. 



