1903.] The Bionomics of Convoluta Koscoffensis, etc. 97 



marine animal. It lives in a film of water, and has migrated, from the 

 sea, shorewards to the highest level consistent with aquatic life. 



The stations occupied by Convoluta are remarkably constant. The 

 constituent patches of a colony may be recognised day after day for 

 months together. Nevertheless, diurnal and fortnightly variations in 

 the size of the colonies occur. 



The diurnal variations are tidal ; each patch reaches its maximum 

 size soon after its site is exposed. The size slowly decreases till the 

 tide comes in. When the tide comes within a few feet, the patch 

 disappears suddenly. At night the colonies do not ascend. 



In addition to its daily variations, Convoluta exhibits a fortnightly 

 lunar variation. The colonies, with their constituent patches, increase 

 to a maximum during spring-tides, and decrease to a minimum during 

 neap-tides. 



The daily variations are due to the tonic effect of light, in which 

 tonic effect must be included the " after-effect " of prolonged light- 

 exposure. 



The fortnightly variations are due to periodicity of reproduction. 

 The majority of animals of a mature colony discharge their eggs in 

 egg- capsules at the onset of the spring tides. The capsules are laid 

 beneath the sand. In most cases the body of the animal is ruptured 

 during the process of laying. The hinder half remains in the sand, 

 the head end rises and joins the patch. Thus at neap-tide the size 

 of the patches and hence of the colony is decreased. 



The colonial habit of Convoluta which distinguishes it from its 

 allies appears to be an indirect result of its tropisms. In obedience 

 to tropic stimuli it becomes adept at vertical movements to the 

 exclusion, in very large measure, of horizontal movements. 



The lethargic state induced by prolonged light and prolonged 

 darkness also tends to preserve groups of Convoluta on the patch to 

 which they belong. Gregariousness is in this view a negative quality. 



REFERENCES. 



1 Geddes, P., " On the Physiology and Histology of Convoluta Schultzii" ' Proc. 

 Roy. Soc.,' vol. 28, 1879. 



2 Von Graff, L., ' Turbellaria Acoela.' Leipzig. Eugehnann. 1891. 



3 Haberlandt, * Uber den Bau u. d. Bedeutung der Chlorophyllzellon von 

 Convoluta roscojfenaix.' Appendix to von Graff's work, pp. 76 90. 



4 Brandt, K., " tJber die inorphologische u. physiologische Bedeutung des 

 Chlorophylls bei Thieren," ' Mittheil. Zool. Stat. Neapel.,' vol. 4, 1883. 



6 Beyerinck, M. W., " Kulturversuche mit Zoochlorellen," 'Botau. Zeitung,' 

 Jalirgang 48, 1890, pp. 745 and 784. 



6 Famintzin, A., " Beitrag zur Symbiose von Algen u. Thieren," ' Memoires de 

 1'Acad. imp. d. Sci. St. Petersburg,' vol. 36, 1889 (Radiolaria and Anemones) ; 

 vol. 38, 1891 (Stentor and Parameciiim). 



7 Georgevitch, " Recherches sur le developpement de la Convoluta roscoffensis," 

 'Archives d. Zool. Experim. et generale,' Ser. 3, vol. 7, 1899. 



