ON MEGASOOLEX CCERULEUS. 81 



which blood is entering the intestiuo-teguraentary system at a 

 certain pressure, which, however slight, would be greater than 

 that in the intestinal capillaries ; into these latter the blood 

 would consequently flow. 



Summary. — The vascular system consists of a portion in the 

 cephalized region, and of other portions metamerically repeated 

 in all succeeding segments. 



The cephalized portion differs only from that occurring in 

 any other segment in having undergone a synthesis, and also 

 in the presence of contractile hearts. 



Throughout the body blood is forced from the contractile 

 vessels into peripheral networks ; thence it is conveyed by a 

 system of intestino-tegumentary vessels to intestinal capillaries, 

 and from these it returns to the contractile vessels.^ 



Nephridia. 



Nephridia are present in the form of minute scattered 

 tubules, and may be seen over almost the entire extent of the 

 body-wall. There are no large tufts of tubules. 



I have not at present worked out the structure of these 

 Nephridia ; they present peculiar difficulties in that they are 

 most minute (actually smaller than in any Perichsete known 

 to me), and at the same time the body-wall, as might be ex- 

 pected from the great size of the worm, is exceedingly thick. 



1 The theory, based upon observations on Megascolex, which I have put 

 forward with regard to the circulation, brings us to such a plausible generalisa- 

 tion, and is borne out by so many structural details, that I cannot help 

 thinking it will be found to have a very general bearing among earthworms, 

 and it may be worth while to speculate for a moment as to the position in 

 the scheme of the subneural vessels possessed by so many worms. So far as 

 I can gather from the descriptions of the relations of such vessels they are in 

 direct connection with the system of contractile vessels, and probably in 

 indirect connection by means of peripheral networks with intestino-tegu- 

 mentary vessels (see Jaquet, 6, p. 340). In this case blood passes into 

 them from the contractile vessels, and ultimately finds its way into intestino. 

 tegumentary vessels and thence to the intestinal capillaries, and they do not 

 thus affect the generalisations made above. 



VOL. XXXII. PART I. NEW SER. f 



