142 PEor. owEisr on the HOMOLoaT 



ing into the cerebral hemispliere, seem to represent the " crara 

 cerebri." They indicate that these so-called cords or tracts, in 

 Vertebrates, may be homologous with the parial cords or tracts 

 girting the gullet and connecting the fore brain (fig. 4, e) with the 

 hinder masses {ih. z) in Invertebrates ; to which pair of intercom- 

 niunioating tracts the oral end of tlie gullet in Invertebrates 

 and the conario-hypophysial tract in Vertebrates hold like 

 relations. 



Such perception of the homologies above indicated led to 

 thoughts of their bearing upon the following higher generali- 

 zation. 



At the period of my student's career in Paris the biological 

 mind was exercised by the question of " Unity of Plan " or " of 

 Composition " in the Animal Kingdom as exemplified between 

 Articulates and Vertebrates by reversing the position of the 

 former, and turning what was regarded the under or ventral side 

 of the crustacean or caterpillar upward, as shown in fig. 3, so as to 

 correspond with the upper or dorsal side of the Eish or Quadruped. 

 The alleged " Law " was further elucidated, as between Verte- 

 brates and Molluskg, by bending a quadruped so as to bring the 

 pelvis in contact with the nape, and so parallelling it with a cuttle- 

 fish — propositions adopted as demonstrativ^e of their " Unity of 

 organic Plan or Composition" by Greoffroy St. Hilaire. 



To the first of these attempts Cuvier opposed the obvious fact 

 that, though the ganglionic cord of the Articulate might be so 

 brought to the relative position, or place, of the spinal cord of 

 the Vertebrate, yet the chief part of the nervous system, or neural 

 axis, universally recognized as "brain " in both, held opposite re- 

 lations to the alimentary canal, being above the mouth in the Ver- 

 tebrate and below the mouth in the upturned Articulate (as is 

 shown in figs. 2 and 3). 



In reference to the second exemplification of the alleged " Unity 

 of Composition," I need only refer to the 'Annales des Sciences 

 Naturelles,' Tom. xix. p. 241, pi. xii. (1830), in which Cuvier 

 refuted Geofiroy's conclusions to his own satisfaction and 

 apparently that of the 'Academie des Sciences,' illustrating 

 his argument by diagrammatic views of the organs which he 

 exposed in an Octopus (fig. 7) and in a doubled-up Quadruped 

 (fig. 8). Among other difficulties which he thereby seemed to 

 demonstrate, was the impossibility of making the brain (figs. 7, 

 8, «) hold a corresponding position in relation to the alimen- 



