144 Wisconsm Academy of Sciences^ Arts, and Letters. 



lum being super-imposed upon the sensory ganglia and the 

 medulla oblongata. This two-ranked arrangement is persist- 

 ent in a more or less marked degree through all the higher orders, 

 rank being indicated by advance from a rectilinear to a curvi- 

 linear arrangement. In the lowest orders in which this 

 arrangement appears, lines drawn through the two series of 

 ganglia are approximately parallel straight lines, in the high- 

 est they are approximately concentric semi-circumferences. 

 This curvilinear arrangement has a double significance. It is 

 the combined result of a tendency to a compact arrangement and 

 a relatively large development of the upper series. 



Much has been said on the relative position of the parts, 

 especially of the cerebrum and cerebellum and more or less 

 significance attached to this principle, yet observation in this 

 direction seems to have been special rather than comprehensive. 



Position with reference to the head of the spinal cord is 

 worthy of especial attention. From a strictly posterior position, 

 the spinal axis passes, as we ascend in rank, through almost a 

 quadrant to a sub-central position beneath. The import of 

 this, as facilitating co-operative intercommunication is appa- 

 rent. 



Embryology furnishes striking facts bearing upon this sub- 

 ject as it does upon other points discussed in this article. But 

 I shall not here insist upon them, for we are, perhaps, not safe, 

 as yet, in assuming that embryological development is along 

 a line of uniform gradational advancement, however true this 

 may be as a general fact. Until there shall be gi'eater uni- 

 formity of opinion as to the origin of species and the relations 

 of embryology to that subject, arguments based upon it must 

 be regarded as questionable to a certain extent. But its gen- 

 eral indications must be allowed considerable value, whatever 

 views of development may be entertained. 



Stated as a deduction, the fourth principle will be. 

 The more compact the arrangement of the parts, the higher the 

 rank. 



