HA'ECKELS SEVEN TYPES OF ANIMALS. 57 



the lancelet need not of itself, however, cause any 

 break in the phylogenetic chain ; supposing for a 

 moment such a chain existed, for, as I have shown, 

 we have in the arthropods a very satisfactory trans- 

 itional link between invertebrata and vertebrata ; 

 whilst from arthropods to mollusks, and downwards 

 among the other subkingdoms of the invertebrata, 

 quite as good transitional links may be also traced. 



Though I thus most freely admit a transitional 

 affinity between invertebrate and vertebrate animals, 

 I repeat that I cannot see in it any corroborative 

 evidence of a descent by evolution of the latter from 

 the former. And as little can I see in the trans- 

 itional affinities among invertebrate animals any 

 evidence of evolution of the higher of them from 

 the lower. 



In his scheme of evolution Haeckel recognises 

 seven types of animals, viz., Protozoa, Zoophytes, 

 Worms, Mollusca, Echinodermata, Arthropoda, and 

 Vertebrata. 



From a branch of Protozoa he represents his 

 hypothetical Gastr.ea to have been evolved. This 

 ancient being, of which the gastrula larva is its 

 recapitulation in characters of remarkable identity in 

 the ontogenesis of the most different animals of the 

 present day, must, Haeckel thinks, have existed in 

 the Laurentian period of the Archolithic time. 



From the ' Gastrsea ' two different lines of the 

 animal kingdom, according to Haeckel, were 



