900 



before the neural ganglia reach them. — The Frog thus 

 affords irrefutable evidence of the real existence of 

 what I call lateral ganglia. — Nor are these ganglia small — 

 indeed in the Frog the lateral ganglia Anlagen greatly 

 exceed those of the neural ganglia in size. Otherwise I 

 may remark the P'rog is one of the most difficult types to study and 

 as long as one possesses such easily obtainable forms as Triton and 

 Salamandra no useful purpose is served by investigating such a highly 

 modified form as the Frog. After this tirade I must say that my apo- 

 logy for treating of the development on Rana at all lies in Spencer's 

 observations on this form. I formerly supported his conclusions but 

 am now fully convinced that they were wrong. 



Spencer described the posterior root of a typical cranial nerve as 

 derived along its whole length from the inner epiblastic layer between 

 the Anlage of the lateral sense organ and the brain or neural tube. 



The ganglion he believed originated at the sensory thickening, 

 and it was thus morphologically the ganglion of the sense organ. 



The mode of formation of nerve and ganglia are in Rana essen- 

 tially the same as in Triton. The sensory epithelium forms a large 

 part, as I mentioned above, but only a part of the ganglion, and the 

 inner layer of epiblast above the neuroepithelium takes no share in the 

 formation of the nerve or ganglion. Except at the neuroepithelium 

 the only place where the inner layer of the epiblast forms ganglionic 

 elements it at the extreme neural limit just outside the neural plate 



— as in other forms. 



In a recent paper Dr. 0. Schultze ^) has given a somewhat 

 diagrammatic figure (fig. 15) of what he calls the „Anlage der Spinal- 

 ganglien in der Kopfgegend" 2) and states that they arise „aus dem 

 peripheren Teile der MeduUarplatte". — I have not the remotest 

 idea what that mass of cells really is which Dr. Schultze represents 

 diagrammatically in fig. 15 — it may turn out to be mesoblast — 

 but this much I do know, the cranial ganglia do not develop in Rana or 

 in any other form in the manner he figures in fig. 15. Dr. Schultze 

 would have done well to have left no. 5 of his „Schlußbemerkungen" 



— that the spinal ganglia develop as stated above — out of his paper 

 until he had proved it, and still better to have left fig. 15 un- 



1) 0. Schultze, Die Entwickelung der Keimblätter und der Chorda 

 dorsalis bei Rana fusca. Zeitschr. f. wiss. Zool., Bd. 47, 1888. 



2) It looks at though Dr. Schultze, like Dr. Onodi, accepted the ho- 

 mology of cranial and spinal ganglia without more ado. 



