MEANING OF THE SYSTEM. 139 



bodies and jointed appendages, with brain and ventral chain of 

 ganglia. 



(6) Alolluscoidea. Bilateral, unsegmented animals with ciliated 

 circlet of tentacles or spirally rolled buccal arms ; either polyp-like 

 and provided with a hard shell case, or mussel-like with a bivalve 

 shell, the valves being anterior and posterior; with one or more 

 ganglia connected together by a perioesophageal ring. 



(7) Molhisca. Bilateral animals with soft, unsegmented body, 

 without a skeleton serving for purposes of locomotion; usually 

 enclosed in a single or bivalve shell, which is excreted by a fold of 

 the skin (mantle) ; with brain, pedal-ganglion and mantle-ganglion. 



(8) Tunicata. Bilateral unsegmented animals with sac-shaped or 

 barrel-shaped bodies, and a large mantle cavity perforated by two 

 openings ; simple nervous ganglion, heart and gills. 



(9) Vertebrata. Bilateral animals with an internal cartilaginous or 

 osseous segmented skeleton (vertebral column), which gives off dorsal 

 processes (the neural arches) to surround a cavity for the reception 

 of the spinal cord and brain ; and ventral processes (the ribs) which 

 bound a cavity for the reception of the vegetative orgai. ; ; never with 

 more than two pairs of limbs. 



CHAPTER V. 



MEANING OF THE SYSTEM. 



VERY different opinions have been held in different places and at 

 different times as to the value of the system. In the last century 

 the French Zoologist Buffon held the system to be a pure invention 

 of the human mind ; while more recently L. Agassiz thought that a 

 real meaning could be attributed to all the divisions of the system. 

 He explained the natural system founded on relationship of organiza- 

 tion as a translation of the thoughts of the Creator into human 

 language, by the investigation of which we become unconsciously 

 interpreters of his ideas. 



But it is clear that we cannot call tliat arrangement, which is 

 derived from the relations of organization founded in nature, an 

 invention of man. Similarly it is preposterous to deny the sub- 

 jective participation of our intellectual activity, since in every system 

 there is expressed a relation of the facts of nature to our comprehen- 



