MEGAZOOIDAL INDIVIDUALS 



87 



tinctly a plan essentially equivalent to that of a continuous 

 " circular " series of tubular zooids whose body-walls are 

 at times in close apposition, and at others incompletely 

 developed. While centrally placed in the circular series, 

 and supported by the best developed " zooidal " walls, is 

 the short oesophagus, representing undoubtedly part of the 

 " main-stem " of an ancestral branching zooidal system 

 (Fig. 23, A). 



Fig. 23. — a, transverse section of a sea-anemone (Adamsia), 

 slightly altered from O. and R.Hertwig. ec, the ectoderm (cross- 

 shaded) ; 1, the mesodermal layer of connective -tissue (shaded 

 dark); en, the endoderm (unshaded); bn, cross-section of 

 one of the longitudinal septal muscles ; s, oesophagus, b, a 

 segment of the body of a sea-anemone (Cereus), traversing the 

 column from the top to the disc (after B. Hertwig) : 6, disc ; 

 *, tentacles : as, oesophagus hanging downwards ; r, r, repro- 

 ductive organs attached to the faces of the mesenteries, 

 (After Nicholson.) 



As a help to make clear the nature of the Sea-anemones' 

 Continuity let us take the following illustration, admittedly 

 a fanciful one, but, considering that evolutionary com- 

 pression has been literally a physical compression during 

 development, not so extravagant as it might at first appear 

 to be. 



Let us picture a primitive Continuously Zooidal Indi- 

 vidual to be modelled in wax, with its main-stem and 



