213 



to Kolster ('98). Most of the observations are fragmentary and all 

 are very incomplete, so that little is known of the occurrence, the 

 distribution or even of the structure of these cells, and almost nothing 

 of the course of their fibres, while their function is as yet a mere 

 matter of conjecture. In only one instance have the neurites been 

 traced. Fritsch ('84, '$6) found that the giant cells imbedded in the 

 anterior part of the cord of Lophius sent their axis cylinders cephalad 

 to the roots of the trigeminus and vagus nerves. 



Two 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 row 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 neurites, all of which run caudad through a pair 

 of fibre bundles which occupy symmetrical positions in the dorsal part 

 of the cord. The neurites were followed but a short distance through 

 the bundle, and their terminations were not made out. The author 

 suggests 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 fluviatilis. The cells are stated to have 

 no dendrites; the neurites were followed but a short distance, the di- 

 rection which they take not being stated. The hypothesis is advanced 

 that they have the function of raising the spines of the dorsal fin. 



There has been a tendency among writers to consider as homo- 

 logous all the colossal ganglion cells occurring in the dorsal part of 

 the cord in the various groups of Ichthyopsida, or to make wide and 

 sweeping generalizations as to their homology; but at the same time 

 the greatest diversity of function has been hypothetically ascribed to 

 them. The diverse conditions described in various fishes and the utter 

 lack of harmony in the homologies made out by different writers, taken 

 in connection with my own observations on many species, I believe, 

 justify the conclusion that these elements present a much greater variety 

 and complexity than has hitherto yet been imagined, and moreover 

 that they are not homologous throughout the Ichthyopsida, nor even 

 within the group of fishes. It is probable, I think, that they have been 

 independently derived in different groups of Vertebrates from less con- 

 spicuous elements, as the occasion for greater size has arisen. 



Methods. 

 The brain and spinal cord were carefully removed from the skull 

 and immediately fixed in one of the following fluids: — 



Anat. Anz. XV. Aufsätze. 15 



