574 PROCEEDINGS OF THE AMERICAN ACADEMY. 



ous system. The rapid method is usually most certain and reliable. 

 Picro-carmine employed after treatment with very dilute osmic acid 

 is suita})le for only the thinnest tissues. Structures much beneath 

 the external surface receive absolutely no fixation, and are therefore 

 quite unreliable for study. 



A Nernst electric lamp, or carefully adjusted direct sunlight, was 

 found to bring into view nerves which it was quite impossible to 

 observe with the ordinary adjustments of light. This is particularly 

 true of methylene-blue preparations of the whole animal, which show 

 plexuses between dorsal nerves, and of tliick Golgi preparations. 

 With such strong light the ner\'es in tliick parts of the body may be 

 seen in situ with surprising clearness. This method has the disad- 

 vantage of soon tiring the eyes. Various methods of dissection were 

 employed on impregnated and stained material for the study of the 

 visceral nerves. 



Dorsal Nerves. 

 A. N^ervcs of the Rostrum. 



Nerve I. — The usually accepted first-nerve pair was first noted by 

 Goodsir ('41), and has been repeatedly described. Owsjannikow 

 ('68) interpreted it as the trigeminus. Schneider ('79) says that from 

 its position the first nerve should be the opticus. Rohon ('82, p. 60) 

 regards the first two pairs of nerves as analogous to the sensory ele- 

 ments of the trigeminus, the third pair to the corresponding (gleich- 

 namigen) facialis of higher vertebrates. Later authors hesitate to com- 

 pare the first nerve with any nerve of the higher \'ertebrates until 

 some facts with regard to its function are established. Dogiel ( : 02) 

 designates the first nerve as purely sensory, since its branches ramify 

 exclusively in the skin. The latter author has described in detail the 

 manner of branching of this nerve in Branchiostoma lanceolatum, and 

 defines the territory which it innervates as the end of the rostrum, 

 with an occasional extension into the adjoining dorsal and ventral 

 skin regions. Dogiel finds some variation in the size and manner of 

 branching of the first nerve. 



* Edinger ( : 06) describes a pair of nerves arising, like an olfactory 

 nerve, from the base of the brain anterior to the nerve pair which is 

 commonly designated as the first. My observations have not brought 

 to light such a nerve, but I do not deny its existence, since I have not 



