248 HAECKEL 



the meaning of these real " social animals." A 

 social medusa has so great an appearance of unity 

 that those who discovered it first did not believe 

 it was a community, but a very complicated 

 individual medusa. Vogt (1847) and Leuckart 

 (1851) had denied this, and declared it to be a 

 social group. But the controversy was still going 

 on, as there was much difference of opinion as to 

 the meaning of " social " and " state." Haeckel 

 now succeeded at Lanzarote in tracing for the first 

 time the development of one of these siphono- 

 phores from the ovum. He was able to show that 

 from the ovum only a single simple medusa is 

 developed. This, then, becomes the parent of the 

 community ; it produces the rest of the members, 

 not by a new sexual generation, but by budding 

 out from itself, until the whole garland of con- 

 nected individuals is ready to constitute the new 

 over-individual, or the community. These lumi- 

 nous investigations were published three years 

 afterwards (1869) in a work that was crowned by 

 the Utrecht Society of Art and Science (The 

 Embryology of the Siphonophorte, with fourteen 

 plates, published at Utrecht). But Haeckel 

 returned time after time in later years to this 

 group of animals with such great philosophic and 

 zoological interest. When he had put before him 

 in the eighties the whole of the siphonophores 

 brought home by the splendid Challenger expedi- 

 tion, he combined the material with the results of 

 his own studies in a fine work, which was included 

 (in English) in the publications of the Challenger 



