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here, although this region has heen investigated not only by the 

 method of sectional series, but also I > v the methylene bine method, 

 by which the investigation is so much easier. By this method 

 Dr. Noordenbos did not find them in the vertebrate skull any more 

 than myself in the skull of Selachians. 



Instead of vertebrae we found the well-known parachordal cart- 

 ilage accompanying the notochord in the occipital and auricular regions. 



Certain authors have indeed spoken of the origin of vertebrae 

 in the occiput, but the parts observed by them, were not cartila- 

 ginous but only badly outlined cell-heaps, not deserving the name 

 of vertebrae. 



So I was greatly surprised when my former assistant, Mr. F. 

 Somes, discovered by the methylene blue method two cartilaginous 

 vertebral bodies in the occiput of embryos of the chick of the sixth 

 breeding day and of ducks in a corresponding stage. 



It will be asked how it is possible that these vertebrae have not 

 been long known, since the embryos of the chick form the classical 

 material for investigation in all embryological laboratories. The 

 answer is that they were not discovered because the stage, in which 

 they appear, is of so very short duration. One has to hit the moment 

 in which the cartilage appears in the first two vertebrae of the neck. 

 Before the cartilage appears in the remaining vertebrae, the two 

 occipital vertebrae have already coalesced with the parachordal 

 cartilage. 



It is impossible to indicate the hour of the breeding day, since 

 the development of the different eggs varies too much. By taking 

 a large quantity of material, however, it is always possible to obtain 

 the desired stage. It would require an immense expenditure of time 

 to work all this material by the sectional method. With the methylene 

 blue method, however, one is ready in a few days. 



So the parachordal cartilage of birds does not originally form a 

 morphological unity. With Sonies we may distinguish two parts in 

 it: an anterior praevertebral part, situated in a region where the myo- 

 tomes are degenerate or abortive and a posterior or vertebral part, 

 occurring in the shape of two vertebral bodies, which soon coalesce 

 with the anterior part. 



Corresponding to these two vertebral bodies later also two vertebral 

 arches appear on each side, which soon coalesce, but the locality of 

 which remains indicated by two openings for the two roots of the 

 nervus hypoglossus 



I'm further particulars ami for several new discoveries about the 

 development of the cartilaginous skull and the spinal column of 



