434 SANGUIFEROUS SYSTEM. 



the sanguiferous system of the radiated classes, a close ana- 

 logy not only to the earliest conditions of this system in the 

 vertebrated animals, but also to the permanent conditions of 

 their chyliferous and lymphatic apparatus, especially in. the 

 composition and properties of the contained fluid, and in the 

 origin and simple structure of the vessels which convey it, 

 and their free anastomoses with each other. The cyclosis 

 which I have long since pointed out in the bodies of polygas- 

 trica, has been more recently mistaken for a revolution of 

 ova, which supposed ova however have never been seen to 

 develope. In the higher forms of these cyclo-neurose ani- 

 mals the afferent vessels may be regarded as veins which 

 proceed, whether from the alimentary canal, or the respira- 

 tory organs, or from the general system, towards the tubular, 

 pulsating, heart- forming portion of the sanguiferous system ; 

 and those efferent vessels may be considered arteries which 

 radiate to the system from this central portion, although they 

 appear still destitute of the strong, fibrous, middle coat, de- 

 veloped in the arteries of higher animals, and the veins are 

 still destitute of valves, and similar in structure to the arte- 

 ries. 



THIRD SECTION. 



Sanguiferous system of the Diplo-Neurose or Articulated 

 Classes. 



The long cylindrical form of the trunk in articulated ani- 

 mals is observed to impress that form on the sanguiferous 

 system, as well as on the nervous, the digestive, and other 

 important internal apparatus, and is marked especially in 

 the longitudinal direction and the elongated form of the 

 great central arterial and venous trunks. The blood is more 

 highly organized and more deeply coloured, provided with 

 more abundant globules and fibrin, in the articulated than in 

 the radiated animals, and is more remarkable for its deep red 

 colour and its extensive distribution through the body in the 

 soft and slow moving helminthoid classes than in the more 

 active entomoid forms. In most of the articulated classes 

 the blood is observed to move forwards in one or more great 



