i] INTRODUCTORY 5 



should serve to induce some of the younger genera- 

 tion of physiologists to devote their attention to a 

 field of research both rich in promise and too little 

 cultivated by the men of science of this country. 



Though the results recorded in this volume are 

 but modest, throwing here and there only a faint 

 light on the problems which they raise, nevertheless 

 they suffice to demonstrate that more skilful observers 

 would, by taking up similar subjects of investigation, 

 make notable contributions to the science of com- 

 parative physiology. 



Having vindicated the importance of research on 

 the lower organisms, let us proceed to our task. 



The plant-animals whose life histories and habits 

 form the subject of this volume are two simple, 

 marine worms, Convoluta roscoffensis and Convoluta 

 paradoxa (Frontispiece). Both are small, though large 

 enough to be seen easily by the unaided eye, and both 

 are conspicuous by reason of their colours. C. ros- 

 coffensis is dark, spinach green, and C. paradoxa 

 yellow-brown. 



Even among worms they occupy a lowly place. 

 Unlike the higher members of this group, C. ros- 

 coffensis and C. paradoxa are unsegmented. Instead 

 of consisting, like garden worms, of a series of ring- 

 like pieces, the bodies of our plant-animals are in one 

 piece and, consequently, bear no ring-like markings 



