M. H. de Lacaze-Duthiers on Phoenicurus. 159 



all parts of the organism. They are in general very slender, 

 very long, and most frequently much undulated, a condition 

 which is in relation to the movements of extension and con- 

 traction of the body. They are divided into two very constant 

 orders. Not far from the ganglia are given off some large 

 trunks, some of which run into the common tissue situated 

 within the muscular layers, which will be referred to further 

 on ; while the others, traversing these layers, are distributed to 

 the subcutaneous tissue and probably arrive at the skin. This, 

 however, is difficult to make out by dissections or sections, 

 and the discovery of these terminations will be purely a matter 

 of chance. 



Studied in a great number of individuals thenerv^ous system 

 presents peculiarities which merit notice. The two superior 

 nerves are stout and terminate suddenly close to the buccal 

 orifice. I shall have to revert to this termination. In their 

 course they give off pretty numerous delicate branches which 

 run into the subcutaneous tissue of the buccal pit. 



The nerves, as they depart from the centre, present from 

 point to point ganglionic inflations of very variable bulk and 

 composed of one, two, or three elongated cells, the larger axis 

 of which is parallel to their direction. 



Another very remarkable peculiarity is the following : — I 

 think I have never met with two individuals presenting a 

 complete identity in the composition of the nervous centres. 

 The following are some of the arrangements observed : — - 

 Sometimes there was only one median ganglion, from which 

 issued the two large buccal nerves and the two principal 

 nerves of the caudal extremity ; sometimes I have only met 

 with a sort of chain of three or four elongated ganglia placed 

 one after the other, a single nerve running towards the mouth 

 and another towards the tail. Lastly^ in one case, I found 

 seven small ganglia arranged transversely and united not only 

 by a transverse commissure, but also by filaments forming a 

 network, a true plexus. In all cases, whatever may be the 

 number of the ganglia, the situation of the nervous system 

 as a whole, with regard to the digestive tube and the muscles, 

 continues the same, and the filaments are distributed in part 

 to the middle of the body and in part to the subcutaneous 

 layers. 



Finally, it is not uncommon to find only a single buccal 

 nerve, and in this case the nerve is stouter ; and I have seen 

 the two buccal nerves issue from the same ganglion. 



To sum up, the position of the nervous system is constant, 

 but its forms vary infinitely. 



I have still to note this fact — I found a transverse cord 



12* 



