184 Journal op Comparative Neurology. 



Lophius, sent their axis cylinders cephalad to the roots of the 

 Trigeminus and Vagus nerves. 



Three recent papers bearing more directly on this subject 

 deserve notice here. Dahlgren '97 finds in the embryos and 

 adults of the order Heterosomata certain giant ganglion cells 

 lying in the median dorsal fissure or in a double rovi^ on either 

 side of the dorsal fissure of the cord, and varying in number 

 from 69 to 500 in different species. These cells give off neu- 

 rites all of which run caudad in two fiber bundles lying 

 bilaterally in the dorsal part of the cord. The neurites were 

 followed but a short distance through the bundle, and their 

 termination was not made out. The suggestion is made that 

 they are connected with sense organs in the fins. Kolster '98 

 describes giant ganglion cells lying in the dorsal fissure of the 

 cord of Perca fluviatiHs. The cells are stated to have no den- 

 drites and the neurites were followed but a short distance, the 

 direction which they take not being stated. The hypothesis is 

 advanced that they have the function of raising the spines of 

 the dorsal fin. Tagliani '97 has described the occurrence of 

 similar cells in Orthagoriscus and Tetrodon. 



There has been a tendency among writers on this subject 

 to consider as homologous all the colossal ganglion cells occur- 

 ring in the dorsal part of the cord in the various groups of Ich- 

 thyopsida, or to make wide and sweeping generalizations as to 

 their homology, although at the same time the greatest diver- 

 sity of function has been hypothetically ascribed to them. A 

 comparison of the very diverse conditions described in various 

 fishes and the utter lack of harmony in the homologies made 

 by different writers, taken in connection with my own observa- 

 tions on many different species, justifies the conclusion that the 

 conditions are much more diverse and complex than has yet 

 been recognized, and that these varied elements are not homol- 

 ogous throughout the Ichthyopsida, or even throughout the 

 group of fishes. Though they may have had a common origin 

 in the ancestral giant cells of worms and crustaceans, they have 

 assumed such very different form, position and function that 

 they cannot be said to be homologous ; and it is perhaps more 



