THE BIONOMICS OF CONVOLUTA ROSCOFFENSIS. 365 



Geddes discovered that Oouvoluta contains a poisonous 

 substance. A dead Convoluta speedily kills a mass of 

 liealtliy individuals if introduced into their midst. This 

 toxic substance may be the means of securing such a patent 

 organism from attack by other littoral animals. Up to the 

 present time the only animal known to prey on Convoluta is 

 a species of PI agio stoma. 



Convoluta roscoffensis offers strong contrasts to other 

 Acoelous Turbellarians. They are short; it is elongated. 

 They are solitary, active, I'etiriug, and odourless ; it is gre- 

 garious, sluggish, and obvious to sight and smell. More 

 striking differences still are those of nutrition. The allies of 

 Convoluta are voracious feeders; whilst it, according to 

 previous investigators, does not feed, but relies, so it is 

 asserted (von Graff, 1891; Haberlandt, 1891; Cleorgevitch, 

 1899), on material manufactured by the green cells which 

 form a dense " tissue" in its body. 



It is not, however, only by reason of its possession of green 

 cells that Convoluta is unique among its fellows. Otlier 

 Turbellarians, and also, as is well known, other animals of 

 various classes, are possessed some of green, some of brown 

 cells, which, it is generally assumed, offer welcome contribu- 

 tions to the diet of the host in which they reside. Its 

 uniqueness consists in this — that as a consequence of, or side 

 by side with, the appearance of its green cells, the habits of 

 Convoluta roscoffensis have become completely different 

 fi'om those of any of its allies. 



Convoluta has been the subject of investigation by various 

 observers, chief among whom are Geddes, Delage, von Graff, 

 IIaberlandt,andGeorgevitch. Gedtles (1879 — 1881) has shown 

 that the green cells contain chlorophyll, that they evolve 

 oxygen in the light, and at the same time store the super- 

 fluous products of photosynthesis as starch. Delage's classical 

 paper (1886) described for the first time the nervous system 

 of Convoluta. Von Graff (1882—1891) has dealt almost 

 exhaustively with its anatomy, and incidentally with the 

 more striking features of its ecology. Haberlandt (1891), 



