CHARACTERISTICS OF THE SUB-KINGDOM VERTEBRATA. 



Sub-Kingdom, Vertebrata^. 



Animals with bilaterally symmetrical bodies, divided internally 

 into two perfectly distinct cavities, one of which is placed dorsally 

 and contains the principal nerve-centres, whilst the other contains 

 the organs of vegetative life. The ventrally-placed cavity of the 

 Vertebrata must be considered to correspond to the entire in- 

 terior of the body of the Invertebrata, and their dorsally-placed 

 cavity, the cerebro-spiual canal, to be without any homologue in 

 the inferior Sub-kingdoms. The motor organs of Vertebrata are 

 directed towards their heart, and point away from their nervous 

 systems, both cerebro-spinal and sympathetic ; whilst in Inverte- 

 brata the motor organs are developed upon the neural aspect of 

 their bodies. Thus the arrangement by which the heart of the 

 Invertebrate animal is dorsal and the nerve-system ventral in posi- 



» In the account here given of the characteristics of each Sub-kingdom and Class, 

 a few general remarks are prefixed to a more detailed zootomical account of each 

 Division. In that account the various organs and systems are treated of very nearly 

 in the same order as that of the ' Physiological Series of Comparative Anatomy con- 

 tained in the Museum of the Royal College of Surgeons in London,' which was fol- 

 lowed by Professor Acland in the arrangement of a large part of the Christ Church 

 Collection now contained in the University Museum. The integumentary and motor 

 organs are first treated of ; then the digestive, circulatory, respiratory and renal ; a 

 sketch of the nervous system is then interposed before the account of the reproductive 

 organs. Objection may be taken to this method of arrangement on the ground of the 

 separation it effects between the motor and the other organs of animal life ; but this 

 theoretical drawback is more than compensated for by many practical advantages. 

 A short notice of any peculiarities in the history of Development, which it may have 

 seemed expedient to add, comes next in order ; and in some cases an account of its 

 subordinate divisions is prefixed or appended to the description of a larger group. 



