xlii 



INTRODUCTION. 



but both shape and contents vary even in different por- 

 tions of the same branch. 



ii. The changeableness and indefiniteness, so to speak, 

 of the system itself, as exhibited in the cord, and more 

 especially in the so-called plexus, are evidence to the 

 same effect. 



The cord or trunk presents the most varied appear- 

 ances, being sometimes simply cylindrical (Woodcut, 

 fig. XV. ec), sometimes composed of a number of anasto- 



Fig. xvii. 



Portion of Branch, showing Cord and Plexus. 

 B. Portion of branch. C. Cord. pi. Plexus. 



mosing strands, sometimes resolved into a wide, irre- 

 gular, open-meshed network *. It also varies in his- 

 tological character, and is frequently charged with gra- 

 nular matter, which completely changes its aspect. But 

 it is in the plexus (Woodcut, fig. xvii. j!>/), so essential an 

 element of the supposed nerve-system, that the irregu- 



* Reichert, ojp. cit. pi. iv. figs. 13 & I.'>, and pi. v. fig. 18. 



