NERVOUS SYSTEM 461 



which are characteristic of all higher Chordates, viz., hair-cells 

 responding to vibrations in fluid ; and very noteworthy is the 

 poor development of the brain, if indeed that term is permis- 

 sible where there is little more than a slight enlargement of the 

 anterior end of the nerve-cord. But when we admit all that, 

 and admit also that Amphioxus shows some similarities to 

 annelid worms, e.g., in its nephridia and in its eye-spots, it 

 remains safe to say that the Lancelets are genuine Chordate 

 animals. 



We give a quotation from a paper by Prof. J. B. Johnston 

 to illustrate the working-out of this argument in detail as 

 regards the nervous system (Johnston, 1905, pp. 125-126). 



" The nervous system of Amphioxus agrees with that of 

 lower fishes in the following respects : — 



" (a) It is dorsal, hollow, and has separate dorsal and 

 ventral roots of definite composition. The canal 

 has an enlargement at the anterior end, the brain 

 ventricle. 

 " {b) The dorsal roots consist of general cutaneous, 

 visceral sensory and visceral motor components. 

 They contain also in the head region fibres of 

 special sense-organs (olfactory or gustatory ?) 

 " (c) Both kinds of sensory fibres have ganglion cells 

 which are situated either within the cord or in the 

 root of the nerve in essentially the same position 

 as the spinal ganglia of vertebrates. 

 " (d) The two kinds of sensory fibres on entering the 

 cord form dorsal tracts similar to those in verte- 

 brates. Many cutaneous fibres show the bifurca- 

 tion characteristic of these fibres in vertebrates. 

 " (e) The viscero-motor cells are situated as in verte- 

 brates dorsal to the somatic motor-cells, lateral to 

 the ventral part of the canal. 

 " (/) The nerve-cells retain the position and characters 

 which are typical in the embryos of vertebrates 

 and which are seen in certain parts of the brain of 

 many fishes. 

 " (g) The ventral roots arise separately and remain in- 

 dependent. They are true somatic motor-nerves." 

 1 1. Our second conclusion is that A mphioxus is a primitive 



