Colonies of Volvox, with small daughter colonies 

 showing within the parental spheres. (General Bio- 

 logical Supply House, Chicago) 



"roll") comes to be understood as the coordinated 

 beating of thousands of flagella protruding outward 

 from the surface of a fluid-filled gelatinous ball. Each 

 flagellated individual imbedded in the outer layer of 

 the jelly ball is something like Chlainydomonas, 

 with an oval body, two equal flagella, a large cup- 

 shaped pigment body, and a red eyespot. If the fla- 

 gella were not in some way coordinated, such a ball 

 could get nowhere and would simply tumble this way 

 and that. If we watch carefully we see that the same 

 end of the sphere is always the one that goes for- 

 ward, and careful study has indeed revealed proto- 

 plasmic strands that traverse the jelly and connect 

 the individual flagellates with each other. Only par- 

 ticular zooids in the rear half of the sphere can divide 

 asexually, while still others produce small motile 

 sperms or large food-laden eggs. Tumbling about 

 within the fluid-filled interior of a Volvox colony are 

 usually to be seen small asexually-produced daugh- 

 ter colonies, which are released to a life of their own 

 when the mother colony breaks down after the spring 

 period of rapid asexual multiplication. In sexual re- 

 production eggs and sperms are not produced at the 

 same time in any one colony, so that whether the 

 species has both kinds of sex cells in one colony or 

 not, fertilization occurs only between sex cells from 

 difi'erent colonies. The resulting fertilized eggs de- 

 velop a thick, spiny covering, often orange or deep 

 red. They lie dormant during the winter months, but 

 in the spring the covering bursts, releasing the young 

 colony. 



THE ANIMAL-LIKE FLAGELLATES 



(Subclass Zoomastigiim ) 



For admission to the clearly animal-like flagellates 

 (the technical name means "animals with whips") a 

 species must lack photosynthetic pigment bodies and 

 must not be otherwise practically identical with one 

 of the green flagellates. It must never store starch or 

 starch-related carbohydrate reserves, and often it 

 will have more than the two flagella that are char- 

 acteristic of most plantlike flagellates. In this group 

 of flagellate orders are many of the important para- 

 sites of man and his domestic animals. 



Most likely to be seen are the free-living Manas 

 and Bodo, abundant among decaying vegetation and 

 in the infusions examined by students. Extremely 

 small, and active in a microscope field, they do not 

 make for easy examination and are usually dismissed 

 quickly as "common monads." Both have two un- 

 equal flagella, but in Bodo the longer one trails be- 

 hind and is used for temporary anchoring. Food is 

 ingested at a spot near the base of the flagella. Oi- 

 komonas. of fresh waters and of soil, is similar but 

 has only one flagellum. Also with one flagellum are 

 the choanoflagellates ("coUar flagellates"), which 

 are generally fixed by a stalk, either singly as in 

 Monosiga, or by a branching stalk that unites many 

 zooids as in Codosiga. There is a large, delicate pro- 

 toplasmic collar around the base of the flagellum. 

 Food particles attracted by currents set up by the 

 flagellum adhere to the outside of the collar and are 

 ingested at its base. 



Important from the human point of view are the 

 trypanosomes, many of which cause serious or fatal 

 disease in man and in his domestic animals. An 

 African form of trypanosome disease has been 

 known to us at least since the days when the slave 

 traders learned not to accept as captives any Negroes 

 with swollen neck glands, an important symptom of 

 African sleeping sickness. A similar disease in cattle 

 is known as nagana. These are not the same as the 

 epidemics of virus-caused sleeping sickness that 

 strike in the United States during certain summers. 

 The African trypanosomes have no doubt been in- 

 troduced into the Western Hemisphere many times, 

 and only the lack of their insect carrier, the tsetse 

 fly, prevents our part of the world from sulTering the 

 dreadful human and economic losses that so heavily 

 afflict Africa. Large parts of Africa have long been 

 uninhabitable for men and for any of their domestic 

 animals except poultry because of certain trypano- 

 somes and the flies that carry them. It has been a 

 long, seesaw struggle, with men now gaining control 

 after many years of intensive medical and ecological 

 work by many investigators. But it remains a stag- 



26] 



