t8o 



PHYSIOLOGY OF THE INVERTEBRATA. 



It may be stated that the oxygen and carbonic anhydride 

 in the blood of the Inrerteh'ata do not behave according to 

 the law of Dalton (the law of partial pressures) in regard to 

 the absorption of a mixture of gases by a simple fluid. A 

 portion of each gas combines chemically with some con- 

 stituent or constituents of the blood. It was Magnus " who 

 first demonstrated that the oxygen and carbonic anhydride 

 of the Vertebrate blood did not obey the law of Dalton ; and 

 the same is true concerning the gases of the blood of the 

 Invertebrata. 



Surveying the Invertebrata as a whole, we find animals 

 like the Protozoa devoid of blood ; next, animals, as some 

 Trematoda and Cestoidea, with blood devoid of corpuscles or 

 solid particles ; then such creatures as the HcJiinodermata, 

 where the blood is corpusculated. In some of these forms, 

 the corpuscles merely consist of solid particles of proto- 

 plasm, devoid of cell walls and nuclei ; while in others the 

 blood contains walled and nucleated corpuscles. In the 

 Myriapoda the blood contains three distinct corpuscles, and 

 during a portion of its course is contained in blood-vessels. 

 In the Crustacea the corpuscles are walled and nucleated, but 

 are colourless, or nearly so ; while in the Gephyrea the cor- 

 puscles have a limiting membrane, nucleus, and coloured 

 contents. 



As a rule, the colouring matter of the Invertebrate blood 

 belongs to the plasma, and not to the corpuscles ; but there 

 are exceptions to this rale, which have already been alluded 



* Poggenclorff' s Annalen, vol. 40, p. 583. 



