OBSERVATIONS ON VARIOUS CELLS 161 



1866 a corresponding structure was also recognised in the 

 ciliated cells of the gut of Anodonta by Eberth and Marchi, 

 and it was shown most convincingly that there was an 

 actual differentiation of the protoplasm in question. 

 Marchi was able to observe a similar fact in the cells of the 

 ciliated epithelium of the labial tentacles and the gills of this 

 mussel. Since that time numerous observers have estab- 

 lished the fact that a striation is widely distributed in 

 ciliated cells, if not present universally. Special mention 

 should be made of the works of Stuart (1867), Arnold 

 (1875), Eimer (1877), Nussbaum (1877), Engelmann 

 (1880), Gaule (1881), and Frenzel (1886). 



Even before these observations upon the cells of ciliated 

 epithelia had been collected, Leydig had already, in 1854, 

 drawn attention to the fact that the non-ciliated epithelial 

 cells of the gut of Isopods had a similar longitudinal stria- 

 tion. Henle (p. 53) and Pfliiger observed in 1866 a 

 partial fibrillation in a longitudinal direction of the proto- 

 plasm of the epithelial cells clothing the efferent ducts of 

 the salivary glands of vertebrata. At a later period numer- 

 ous investigators, especially Pfliiger (1869 and 1871), and 

 Heidenhain (1868, p. 21 ; 1875), occupied themselves 

 in extending these observations. It was established thereby 

 that the striated structure of protoplasm is a phenomenon 

 of very widespread, in fact one might say of almost universal 

 occurrence in the columnar epithelial cells of the skin, 

 intestine, and numerous glands. 



As has been remarked above, Frommann and Arnold had 

 really only observed more or less isolated filaments, which 

 here and there showed a net-like union. Frommann's more 

 far-reaching supposition was a hypothesis, the correctness of 

 which could only be proved by future observations. The 

 works that appeared soon afterwards were evidence of the 

 correctness of this supposition. Pfliiger found (1869) that 

 the protoplasm of liver cells was fibrillar, and in his detailed 

 work the structure is even represented as a beautiful fibrous 

 network, since the fibres are made to anastomose with one 

 another. It is interesting also to find that he expresses 

 himself to the effect that the fibrillar axis-cylinders, which 



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