FIG. 8. Parts of three cells on the epidermis of a larva of Amblystoma punctatum. 

 The nucleus with a prominent envelope is shown at the lower right. The cytoplasm 

 shows several profiles of the ER, some with particles attached (rer) and some 

 separate, agranular profiles. The dominant feature of these cells is a large number 

 of fine filaments representing the keratin component of the cells. These filaments, 

 in places assembled in bundles (K), occupy the continuous or matrix phase of the 

 cytoplasm. The arrow marks a desmosome (D), which represents a point of attach- 

 ment between two adjacent cells; (is) indicates intercellular spaces. 



This cell, which can be classified as a retaining or nonsecretory type of cell 

 (Mercer, 1961) may ultimately show more and more keratin and less ER, until at 

 the end of its differentiation it is practically free of ER except for the nuclear 

 envelope. Magnification: 22,000 X. 



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