History of a transieut nervous apparatus in certain Ichthyopsida. 327 



Similar cells first attracted my notice when commencing work on 

 Lepidosteus in 1888. What was then made out concerning them 

 was subsequently published in a preliminary notice ^ ). These ganglion- 

 cells were found to occur in large numbers in the embryos of all the 

 oviparous Ichthyopsida examined, i. e. in Lepidosteus, Scyllium^ Pri- 

 siiurus, Raja, Labrax, Esox, Rhodeus, Salmo, JPetromyzon, Rana and 

 Triton. In all of these at certain periods of the development the 

 ganglion-cells were found lying at the dorsal summit of the cord, ex- 

 tending backwards from the hypoglossus region. Some of the obser- 

 vations there recorded are confirmatory of the earlier ones of Rohon 

 in the trout, i. e. that they are the first cells to take on ganglionic 

 characters, that they are multipolar etc. (see p. 116). 



As of some importance the occurrence of a few such cells in 

 Mustelus vulgaris was commented upon, and agreement was expressed 

 with Mater in stating their absence in Torpedo"^). It was, 

 moreover, established that they were of transient nature, and their 

 degeneration and atrophy were briefly described. Finally, it was 

 suggested that Kleinenberg was probably in the right in his 

 suspicion that these cells might be analogous to certain subumbrellar 

 cells in Lopadorhynchus which "introduce" the development of the 

 ventral nerve-cord. 



In 1891 DoHRN •^) published an important "Studie" on "Nerven- 

 faser und Ganglienzelle". In the text these transient ganglion-cells 

 received no description, but a number of figures of them, presenting 

 appearances at that time very familiar to myself, were given on 

 tab. 22. And on p. 310 Dohrn remarks : 



"Es war anfänglich meine Absicht, schon in der vorliegenden Studie 

 diese Frage nicht nur für die peripherischen, sondern auch für die 

 centralen Ganglienzellen zu erörtern, und mich durchaus für eine spe- 

 cifisch nervöse und gegen jegliche Art von ausschliesslich trophischer 

 Function der Ganglienzellen zu erklären. Ich hatte zu dem Behufe 

 bereits einen Excurs auf die Verhältnisse des Centralnervensystems 



1) No. 2, p. 115—118. 



2) The system appears to be not entirely absent in Acanihias, for 

 in very early embryos transient ganglion-cells and a few small nerves 

 are met with. 



As far as can be judged, without fuller investigation, the apparatus 

 is very feebly developed in Acanthias and very evanescent in cha- 

 racter. Further details may be reserved for Part II of the work. 



3) No. 5. 



