SEGMENTAL INDIVIDUALS 



117 



representing the manubria of the medusoids about to be 

 perfected, and the future separate water-vascular systems 

 are in continuity to form a temporary system for the whole. 

 If therefore we imagine that a primitive type with general 

 characters like those of Aurelia stopped at strobilation, 

 and did not throw off its " segments " as medusoids, but 

 that these as they matured were modified to form indivisible 



Fig. 42. — Illustrating theory of the earthworm's evolution. 

 A, general plan of a medusoid. b, plan of imaginary series 

 of such medusoids which by developing in close continuity have 

 lost separate identity, c, the imaginary organism, b, with a 

 mouth, m, developed at what becomes the anterior end ; and 

 with its successive circular canals encroaching, along with 

 successive vela, to encircle closely the digestive tube, toe, the 

 " open " coelom of a, is now in c the closed coelom shut in by 

 the encroaching velum, vel. d, diagrammatic plan of anterior 

 segments of earthworm's body, showing successive subdivisions 

 of the ccelom, the dorsal vessel, and its five hearts encircling 

 the digestive tube, m, mouth ; 1, 2, 3, etc., the segments. 

 (Also see Fig. 57.) 



parts of one organism, we would have a picture of a primitive 

 Segmental Individual. 



In such a one we would expect a distinct amount of 

 repetition of circulatory, nervous and reproductive parts 

 or organs, and that the plan and arrangement would clearly 

 reflect megazooidal derivation ; and, if our suggestions are 

 sound, we should recognise these features in a typical 

 annelid like the earthworm. Our primitive segmental 

 organism would clearly be aquatic and free-swimming, 



