the narrow neck of the flask there emerges the single 

 long flagellum. Into the rounded base of the flask a 

 large contractile vacuole discharges its fluid content 

 at frequent intervals. No one has ever seen a green 

 euglena take particles of food into its gullet, but if 

 placed in the dark the animal does lose its green pig- 

 ment, chlorophyll, and lives by absorbing nutrient 

 material through the surface. Next to the gullet is a 

 bright red eyespot, and if a dish of euglenas is placed 

 near a window they gather quickly in the lighted side 

 of the dish if the light intensity is not too great. They 

 are negative, however, to very strong sunlight. 



This special sensitivity to light plays a major role 

 in the life of animals that must use the energy of sun- 

 light to synthesize their food supply. Euglemi gracilis 

 is small as euglenoids go, '-,,10 of an inch, and the 

 flagellum is shorter than the body. It is one of the 

 most common species, apparently because it can 

 adapt to a wider range of acid or alkaline conditions 

 than can others. Euglena rubra contains thousands 

 of red granules, which may be concentrated in one 

 central area, allowing the green color of the pigment 

 bodies to predominate, or which may be distributed 

 through the protoplasm, covering the green bodies 

 and giving a red color to the animal and to the scum 

 it forms on barnyard ponds, especially in very hot 

 weather. During sunlight hours a pond may appear 

 red, then turn green when the sun goes down. Color- 

 less euglenoids live by devouring bacteria, algae, 

 diatoms, and the smaller protozoans. Reproduction 

 in Euglena is by asexual fission only, with the body 

 splitting down the middle and parallel to the long 

 axis of the body. Division may occur in the free- 

 swimming animal, but the encysted reproductive 

 stage is so common that it may be the sole content of 

 the green scum covering a pond. If examined under 

 a microscope it looks more like an alga. 



THE PHYTOMONADS 



The most plantlike of the flagellates are the phyto- 

 monads ("plantlike units'"), which resemble algae in 

 having, typically, a rounded shape, a rigid cellulose 

 wall, and grass-green pigment bodies. Chlamydo- 

 monas is common in ponds and ditches and often so 

 numerous there as to render the water an almost 

 opaque green. Especially abundant in waters con- 

 taminated by manure, it probably supplements its 

 mostly photosynthetic nutrition with saprophytic 

 feeding, absorbing dissolved nutrients through the 

 body surface. It is small ('i-.-,,, of an inch), ovate, 

 has two equal fiagella protruding through the cellu- 

 lose cell membrane, a red eyespot, and a large cup- 

 shaped pigment body. Carteria resembles Chlainy- 

 clotnonas but has four fiagella. It is probably a 

 species of this genus that lives in the tissues of the 

 marine acoel flatworm Convoluta roscoffensis (Plate 





J 



o 





<. ■- ■ ■ ■"-* • 



■W 





Eunlena, in the midst of dividing, shows a split front 

 end, each half with a long flagellum. A smaller flagel- 

 late, Peranema, is at the right. (Ralph Buchsbaum) 



36). Haematococcus looks like a reddish Chlamy- 

 domonas with a loosely fitting outer wall that is at- 

 tached to the organism by radiating threads of proto- 

 plasm. Its red hematochrome granules may be so 

 numerous as to mask the green, giving a red color to 

 standing rain water or to fresh-water ponds in which 

 Haematococcus abounds. In the Alps and in the 

 American Rockies Haematococcus is well known for 

 imparting a reddish or pinkish color to melting snow 

 drifts. 



Colonial phytomonads, all fresh-water forms, are 

 remarkable for the way in which the various species 

 can be arranged in a series showing every stage from 

 a simple flat disk of four cells, as in Gonium, that 

 look alike and reproduce in the same way, to com- 

 plex colonies of many thousands of cells, as in Vol- 

 vo.x. where cells differ in appearance and in function 

 yet are coordinated into a single behavior unit. 

 Though developed to a lesser degree, these are cer- 

 tainly the beginnings of the multicellularity and the 

 individuality we see in higher plants and animals. 

 Volvox is large enough ( 'i,, of an inch in diameter) 

 to be seen in fresh-water ponds as a small green ball 

 that rolls smoothly through the water. Under the mi- 

 croscope this rolling motion (lo/vere is Latin for 



[25 



