Respiration in Invertebrate Animals. 343 



chylaqueous fluid is present everywhere, and immediately under- 

 neath the cuticle. It moves to and fro in its vacuoles. It is the 

 immediate recipient of the external oxygen. It imparts it se- 

 condarily to the true blood, if this exists. Future science may de- 

 monstrate that the properties of oxygen are intensified (ozom'ze^/?) 

 by passage through, or absorption by, a living fluid. Deep 

 meaning may yet radiate from material collocations, over which 

 now chaos broods. 



It is a remarkable fact, that the body of every Entozoon, 

 whether imbedded in the parenchjTua of solid organs or lodged 

 in the cavitary- viscera, is immersed in a reservoir of fluid. The 

 Tdenice and Bothriocephali are apphed closely to the walls of the 

 intestine (the orifice of each segment being adherent to the in- 

 fested surface and surrounded by a mucous capside filled with 

 fluid). This fact is easily verified in the instance of those species 

 of Cestoid worms which inhabit the intestine of fishes, birds and 

 reptiles*. 



The Fluke swims in a pool in the biliary ducts of the sheep. 

 The Trichina in the substance of a muscle floats in a reservoir 

 of fluid, and the Filaria in the cellular tissue is surrounded by a 

 stratum of serous liquid. These enveloping fluids are efiiised by 

 the living vessels of the part upon which the animal preys. These 

 circumstances present a fact which demonstrates that the life of 

 Entozoa is essentially aquatic. The fluid is no essential consti- 

 tuent of the organism of the parasite. It is extravasated by reason 

 of the irritation excited by the presence, the worm on a living sur- 

 face, or in the midst of a living organ. It is however a fundamental 

 condition of existence. It is the medium of respiration to the En- 

 tozoon. How could this \-ital process occur if the animal were 

 surrounded by a solid substance ? The fluid contained in these 

 cysts must be frequently renewed, because the blood-corpuscles 

 revealed in it by the microscope are always fresh in appearance, 

 plump and perfect in outline. This fact also proves that it is 

 derived directly from the blood of the infested animal ; it is there- 

 fore charged with oxygen in the same proportion as the latter. 

 Thus is explained an important external condition of respiration 

 in the Entozoa. 



The Nematoid Entozoa (figs. 10, 11 & 12) are distinguished 

 from the parenchymatous orders in one essential respect. In the 

 Nematoidea the viscera float more or less freely in a spacious cavity 

 filled with fluid. They agree in organic type with the cylindriform 



* Bothridium Pythonis inhabits the large intestine of the Cod. 

 Acanthobothrium coronatum is found in the intestine of the Ray-fish. 

 Trienophorus nodulosus lodges itself on the peritoneal surface of the 

 liver of the Perch. 



Floriceps saccatus in the intestine of many fishes, &c. 



