78 ON THE MORPHOLOGICAL RELATIONS 



V. ON THE MORPHOLOGICAL EELATIONS OF 

 THE NEEVOUS SYSTEM IN THE ANNULOSE 

 AND VEETEBEATE TYPES OF OEGANISATION.* 



THE term annulose is employed provisionally, and in a 

 morphological sense, as including all animals possessing a 

 ganglionic nervous collar and axis, and presenting, at the 

 same time, more or less distinct indications of a segmented 

 structure of body. 



Physiologists appear generally inclined to consider the 

 central portions of the annulose and vertebrate nervous sys- 

 tems as modified forms of the same arrangement. These 

 forms are held to possess a general similarity of structure, 

 and correspondence in function ; and the ganglionic collar 

 and axis of the annulose are assumed to be homologous either 

 with the cerebro-spinal axis, or with the series of ganglions 

 on the posterior roots of the spinal nerves, or with the system 

 of sympathetic ganglions of the vertebrate animal. 



In my own examination of this subject I have been 

 strongly impressed with the necessity of determining the 

 morphological character of the cesophageal collar, and the op- 

 posite positions of the so-called brain and abdominal gan- 

 glionic cord, before any satisfactory advance could be made 

 in ascertaining the relations of the two forms of nervous 

 system. The apparent morphological difference between 



* This and the two following papers were read to Section D at the Chel- 

 tenham Meeting of the British Association, Aug. 5-12, 1856, and were pub- 

 lished in abstract in the Edinburgh Philosophical Journal, Jan. 1857. EDS. 



