Franklin P. Mall 



335 



coarse network. In the mandibular arch all stages of embryonal con- 

 nective tissue are seen, from single cells of mesenchyme, closely crowded 

 together immediately below the ectoderm, to a complete syncytium 

 lying deeper in the tissue. The single cells which are closely crowded 

 undoubtedly form a growing point from which the syncytium arises. 

 In the tail there is a very dense connective-tissue syncytium, more so 

 than around the anterior end of the chorda. The nuclei are encircled 

 with endoplasm which radiates over the exoplasm in all planes. Within 

 the endoplasm there are imbedded numerous yolk discs and pigment 

 granules; there are also some single yolk discs scattered throughout the 





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m^'j^ 





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Fig. 3. 



Fig. 3. Mesenchyme around the anterior end of the chorda in a tadpole 6 mm. 

 long ( X 500 diameters). 



Fig. 4. The same in a tadpole 9 mm. long. 



exoplasm, especially in the neighborhood of the yolk of the embryo. 

 This condition occurs before the circulation of blood is well estab- 

 lished, and indicates that the nutrition of the syncytium of the tail is 

 carried on in part by the inwandering of cells from Uie yolk of the 

 ernbrj'o. 



In a stage somewhat older than the one just described, just after the 

 mouth has broken through, the connective-tissue syncytium around the 

 anterior end of the chorda is practically completed. Most of the 

 nuclei, with a small amount of endoplasm around them, lie upon the 

 exoplasm of the syncytium at its nodal points. Within the head in 



