84 SECTIONAL ADDRESSES. 



was possible. That this speculation of Church's represents what was 

 actually accomplished, even though it does not make clear the means 

 by which it was brought about, is shown by the interesting researches 

 of Wager * on the rise and fall of the more highly organised flagellate 

 Euglena. Euglena is a somewhat pear-shaped flagellate, the tapering 

 end being anterior and provided with a single fiagellum, which 

 acts as a tractor drawing the organism towards the light. Tha 

 posterior end carries the nucleus and most of the chlorophyll and 

 food reserves. The whole organism has a specific gravity of 

 1.016, being slightly heavier than the fresh water in which it lives. 

 When dead, or when the fiagellum is not moving, it takes up, under 

 the action of gravity alone, a vertical position in the water, with the 

 pointed anterior end uppermost, and the heavier, rounded, posterior 

 end below, and sinks gradually to the bottom. 



In a very crowded culture a curious phenomenon is seen, because 

 the organisms tend to aggregate into clusters beneath the sm-face film, 

 and when they are crowded together in these clusters the flagella cease 

 to work. Tliis makes the whole cluster sink to the bottom under the 

 action of gravity. When the bottom is readied the individuals are 

 spread out by the action of the downward current, and, when they are 

 sufficiently widely apart, the flagella again begin to move, carrying the 

 organisms in a more diffuse stream once more to the surface. The 

 whole culture vessel becomes filled with a series of vertical lines of 

 closely aggregated falling organisms, surrounded by a broad cylinder 

 of disseminated swimming ones, rising to the surface by the action 

 of their flagella. If the conditions are kept uniform such a circulation 

 of Euglenas, falling to the bottom by gravity w^hen the flagella are 

 stopped and returning to the surface under their own power, will 

 continue for days. 



The fiagellum in this species, therefore, retains its most primitive 

 function of drawing the organism to the light in the surface layer. 

 With the establishment of the fiagellum an organ is produced which 

 shows remarkable persistence in both the animal and vegetable kingdoms, 

 and from the existence of tlie flagellated spermatozoon in the higher 

 vertebrates, in accordance with Haeckel's biogenetic law that the indi- 

 vidual in its development repeats or recapitulates the history of the 

 race, we conclude that they also' in their earliest history passed through 

 a plankton flagellate phase. 



Exactly at what stage in the history of the autotrophic flagellate the 

 first formation of chlorophyll and its alHed pigments took place we 

 have no means of determining, but it may have been before even the 

 flagellum itself had begun. This advance and the subsequent concen- 

 tration of the pigments into definite chromatophores or chloroplasts 

 doubtless immensely increased the efficiency of the organism in pro- 

 ducing the food which was necessary to it. The recent work of Baly 

 and his collaborators becomes here again of the first importance, and 

 though the subject of the part played by chlorophyll in photosynthesis 



» Phil. Trans. Roy. Soc, vol. 201, IfMl ; and Srlcnce Progress, vol. vi . 

 October 1911, p. 298. 



