KUTCHIN. — PERIPHERAL NERVOUS SYSTEM OF AMPHIOXUS. 579 



are probably as frequent in one form as in the other. Hatschek ('92, 

 Fig. 6) figiu'es a branch of nerve II as passing to the deeper nerve 

 plexus of the mouth. I have never observed such a branch, but am 

 aware that variations occur. However, such a condition can scarcely 

 be the typical one. Nerves I and II usually send no branches to deep 

 lying structures. 



No new observations concerning the olfactory pit were made in the 

 present study, and this structure has not been included in the enumera- 

 tion of the dorsal nerves. 



With regard to the spinal or cerebral character of the more anterior 

 dorsal nerves, and especially those having no ventral roots, there has 

 been much variation of opinion. Owsjannikow ('68) and Stieda 

 ('73, p. 48) designate the first two nerve pairs as cranial. Stieda, 

 however, denies the existence of nerves of special sense. Langerhans 

 ('76, p. 279) says that the first and second nerves are distinguished 

 from the others by the possession of peripheral ganglion cells, as well 

 as by their origin. Schneider ('79, p. 14) regards the first and second 

 nerves, and the bulbus olfactorius as cranial, but considers it uncertain 

 whether they differ in function from the remaining sensory nerves. 

 Rohde ('88) calls the first five sensory nerve pairs cerebral. It does 

 not fall within a discussion of the distribution and structure of the 

 peripheral nerves, to treat of the question as to the cranial or spinal 

 character of the more anterior dorsal nerves. The structure of the 

 neural tube, and the functions of these nerves must enter largely into 

 such a determination. If, as Hesse ('98) states, the whole spinal cord 

 reacts to light stimulation, we may well make careful investigation of 

 the physiological character of the more anterior nerves, before as- 

 cribing any special degree of cephalization to Amphioxus. Heymans 

 et van der Stricht ('98, p. 68) say, in regard to this question, that the 

 anterior extremity of the spinal cord of Amphioxus might perhaps be 

 considered anatomically as a head (in its first stage of development), 

 but that physiologically the head perhaps extends over the whole 

 nerve axis, though especially developed in the segment corresponding 

 to the buccal and branchial region. 



B. Nerves of the Buccal Region. 



Nerve III. — The third dorsal nerve usually sends a small branch, or 

 branches, to the posterior part of the rostrum, but by far the greater 

 part of its branches are confined to the buccal region. It may, 

 therefore, be properly included with the nerves of this group. 



