THE. BIONOMICS OF CONVOLUTA ROSCOFFENSIS. 371 



body. Tliese nre the remaiiis of green cells from wliicli tlio 

 digestible portions have been removed (PI. 31, fig-. 7). 



The general features of the nutrition of Convoluta 

 roscoffensis may be stated in the following manner : — In 

 the embryonic and early larval stage, the animal feeds upon 

 its reserve materials. After hatching, it is for a time — that is, 

 up to time of functioning of the green cells — heterotrophic. 

 It then passes through a long period, during which it subsists 

 on diatoms and other ingested substances, possibly also on 

 organic food derived from its green cells ; that is, assuming 

 tliat Convoluta adopt both these methods, it is myxotrophic. 

 Finally, in the mature stage, it derives all its food from the 

 green cells directly by digesting them, and possibly also 

 indirectly by extricating plastic material from them. Up to 

 the present, however, there is no evidence that Convoluta 

 derives any food by the last means. 



It is often assumed that the number and variety of forms 

 of life are diminished in the upper pai-t of a sand}^ shore as 

 compared with the more continuously submerged lower zones 

 of the beach. Von Graff, for example, when referring to the 

 abstention of Convoluta roscoffensis from food, states 

 that its " life in sterile sand is, at all events, unfavourable to 

 the assumption that Convoluta feeds on an animal diet " 

 (1891). Convoluta, however, does not live in sterile sand. 

 The variety and numbers of the fauna and flora of the 

 Convoluta zone is remarkable. Foraminifera and ciliate 

 Protozoa, Nematodes, Copepods, and Turbellarif> are the chief 

 and most constant forms of animal life; whilst bacteria, 

 diatoms, brown and green algee of simple forms, are the 

 main kinds of vegetable life. In addition to these sources 

 of food, the rich grazing grounds provided by Convoluta 

 itself must be mentioned. We refer in Sect. V to the 

 formation of the egg-capsules simultaneously by large 

 numbers of a colony, and to the concomitant casting off of 

 the hinder end of the body. The capsules attract large 

 numbers of diatoms, and in time become almost covered 

 ^vith colonies of simply organised algal colls. The detached 



