VERTEBRATE NATURE OF MAN. 253 



important and essential to the reader, are shown by the 

 History of Evolution and Comparative Anatomy to be of 

 secondary and subordinate importance, or even entirely non- 

 essential. For example, from this point of view the head 

 with the skull and the brain are non-essential, as are also the 

 extremities, or limbs. It is true that these parts of the body 

 possess a very high — even the very highest physiological 

 importance; but for a morphological conception of the 

 Vertebrate, they are non-essential, because they appear 

 only in the higher Yertebrata, and are wanting in the lower. 

 The lowest Vertebrates possess neither a clearly marked 

 head with a brain and skull, nor extremities, nor limbs. 

 The human embryo also passes through a stage in which it 

 possesses no head, no brain, no skull, in which the trunk 

 is still entirely simple and undivided into head, neck, 

 breast, and abdomen, in which there is no trace of limbs, 

 arms, or legs. In this stage of evolution, Man, as well as 

 every other higher Vertebrate, essentially resembles that 

 simplest Vertebrate form, which is represented only by a 

 single existing Vertebrate, retaining the form throughout 

 life. This single lowest Vertebrate, which deserves the 

 closest consideration, and, next to Man, must undoubtedly 

 be called the most interesting of all Vertebrates, is the well- 

 known Lancelet, or Amphioxus (Plates X. and XL). As we 

 shall afterwards examine this animal minutely (in Chapters 

 XIII. and XIV.), I shall say but little about it now. 



The Amphioxus lives buried in sea-sand ; it attains a 

 length of 5-7 centimetres, and in its adult condition is 

 shaped exactly like a long, lanceloate leaf. It it>, therefore, 

 called the Lancelet. The narrow body is compressed on 

 \>oth sides, is similarly pointed in front and at the back. 



