364 F. W. GA5IBLE AND Fh'EDERTCK KEEBLE. 



PAGE 



Section V. — Ecology of Convoluta .... 407 



1. Position of the Colonies of Convolula . . . 407 



2. The Factors tiiat regulate the Formation and Position of the 



Colonies ...... 410 



3. Variations in the Constituent Patciies of a Colony . . 412 



4. General Phenomena of Reproduction and Development . 414 

 Section VI. — Summary ..... 418 

 Section VII. — Literature ..... 424 

 Section VIII. — Explanation of the Pl.\tes . . . 428 



Section I. — Introduction. 



Convolnta roscoffensis is a green Tnrbellarian peculiar 

 to Brittany, along whose coasts it is distributed intermittently. 

 It is a slender, elongated, ciliated Avorm of sedentary, 

 gregarious liabit. 



Though the individual Convolnta is, on the average, not 

 more than 4 mm. in length, it occurs in such vast numbers as 

 to form conspicuous, dark, " spinach-green " patches on the 

 shore. These patches, lying well up the beach within the 

 tidal range, may be so small as to be barely recognisable, or 

 so big as to form an almost continuous band, extending over 

 fifty or even a hundred yards. The general rule, during the 

 summer, is for colonies o£ Convolnta to occupy a number of 

 well-defined, isolated stations separated from one another by 

 barren stretches. Each colony consists of one patch or of a 

 group of patches. 



At niorht, the colonies sink beneath the surface of the sand 

 even at low tide ; only on bright moonlight nights may a few 

 individuals of a colony be met with on the surface of the 

 sand. During daylight the colonies rise up from below 

 ground, and appear on the surface soon after the ebbing tide 

 has left it. There they remain, the colony as a whole inert, 

 but many of its inhabitants in active movement within its 

 borders, till tlic returning tide covers, or is about to cover 

 them. 



The strong characteristic odour of Con vol uta affords a 

 means of detecting" colonies too small to be seen. 



