2 1 o Traces of Unity in the Personal, 



form of life. It arose in the Laurentian epoch by spon- 

 taneous generation from inorganic matter. Its accept- 

 ance as our earliest ancestor is necessary ' on the most 

 weighty general grounds.' 2. The Amoeba ; and 3. The 

 Compound A mcebcs come next. They are to be accepted 

 on embryological considerations ; as also are 4. The 

 Planceada, represented by some ciliated animalculae. 

 5. The Gastraa (Urdarmthiere) are a purely imaginary 

 class of animals. They are placed here because required 

 as ancestors for the Gastrula, itself an imaginary order, 

 derived from embryological exigencies. 6. The Archel- 

 minthes, or earliest worms, represented now by the 

 Turbellaria. 7. The Scolecida, the actual annelidan 

 representatives of which are not known. 8. The Chord- 

 onia, also a purely imaginary type, having no extinct 

 or living representatives, but being ' undoubtedly ' the 

 progenitors of all the Vertebrata, through the Asci- 

 dians. 9. The Acrania, represented by the Amphi- 

 oxus, the lowest form of vertebrate animal, a rudimen- 

 tary fish, having certain resemblances to the Ascidians. 

 10. The Monorhina which was the parent stem of the 

 sharks, through the Amphirhina, represented by the 

 modern lampreys. n. The Selachit, or skark-tribes, 

 from which sprang 12. The Dipneusta, or Lepido- 

 sirens, from which originated 13. The true Amphiuma, 

 and 14. The Sozura, another order of Amphibia, inter- 

 polated here, ' because required as a necessary transition 

 stage between the true Amphibia/ and 15. The Prot- 

 amniota, or general stem of the mammals, reptiles, and 

 birds. " What the Protamniota were like," says Pro- 

 fessor Huxley, " I do not suppose anyone is in a posi- 

 tion to say," but they are proved to have existed 

 because they were the necessary forerunners of 16. 

 The Pro-mammalia, the earliest progenitors of the 



