426 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1960 



celled animals unite in pairs like spennatozoa and eggs, forming 

 zygotes. 



Now comes the remarkable part of the history of tliese strange 

 creatures. The zygotes are essentially living protozoons. Where 

 many are assembled on the water, as they meet one another they unite 

 in large numbers and fonn a new Plasmodium. The result is not an 

 aggregate of cells, but a complete fusion and blending of the zygotes 

 into a protoplasmic mass, in which only the nuclei remain distinct. 

 Nothing like this occurs elsewhere in the whole realm of nature. No 

 outside force brings the zygotes together; it is as if these tiny bits of 

 protoplasm have an instinct to unite, or is it merely chemical attrac- 

 tion? Wells, Huxley, and Wells (1934) liken the Plasmodium to the 

 whole human population of a town fused into a great mass of living 

 substance, which then creeps about as a single creature. This would 

 be socialism carried too far for its strongest advocates. Here, on the 

 very lowest level of life, we find the most complete surrender of the 

 individual to the community. 



VOLVOX 



Among the Protozoa there is an interesting fresh-water colonial 

 form named Volvox. It consists of hundreds or thousands of minute 

 biflagellate one-celled individuals, or zooids (zo-oids), set closely on 

 the periphery of a gelatinous sphere, as much as 2 millimeters in 

 diameter. The vibratile threadlike flagella of the zooids project from 

 the surface and cause the sphere to move through the water. Very 

 surprisingly, the action of the flagella is so coordinated that the colony 

 always moves with one pole forward. Volvox reproduces both asex- 

 ual ly and sexually. In the first form, a zooid divides to form a 

 miniature colony inside the parent, which then breaks out through 

 the wall. In sexual reproduction some zooids enlarge to become the 

 equivalent of eggs, and others divide to form spermatozoa. The two 

 forms of gametes then unite in pairs as zygotes, which by repeated 

 division form new colonies. 



The zooids of the Volvox colony are perfect protozoan individuals, 

 and yet they never know an independent life. They are but little 

 differentiated, except that the anterior zooids are smaller and non- 

 reproductive. Since the body of a metazoic animal may be regarded 

 as a society of differentiated cells, it has been suggested that the 

 Volvox colony shows how the many-celled animals may have been 

 derived from Protozoa, and the globular Volvox colony has even been 

 likened to the blastula stage of a metazoon. However, it is not con- 

 tended that Volvox is ancestral ; it is simply an imitation blastula. As 

 a motile colony of closely adherent individuals it is unique. 



