134 BULLETIN OF THE ESSEX INSTITUTE. 



from the fact that I have not found them to appear as in- 

 dependent cartilages in any of the forms studied. This 

 may, in some cases, be due to the fact that the inde- 

 pendent condition is limited to the pro-cartilage stages or 

 to the incompleteness of my series of embryos. But I 

 feel confident that the parts mentioned do not appear as 

 independent cartilages in Amblystoma. The existence of 

 such a condition as that shown in Fig. 18, where there is 

 no sign of cartilage near the median line, and the appear- 

 ance of a complete tectum in an embryo but little older 

 form the basis of my conclusions in regard to the synotic 

 tectum. My evidence as to the formation of the trabecu- 

 lar crests and the ethmoid plate is of the same nature and 

 shows them to be outgrowths from the primitive trabeculse. 



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