162 PROTOPLASM 



are stated to be in direct connection with the liver cells, 

 expand into these cells by anastomosis of their fibrillae. The 

 networks drawn and described are rather coarse, as was in 

 general the case with all the early observations upon proto- 

 plasmic structures ; on which account we can only be dealing 

 in all these observations with a part merely of the true 

 structure, that is to say, in all probability with a coarsely 

 vacuolar structure in certain protoplasms a point which 

 cannot now be decided with certainty in many cases. 



In 18*70 Kupffer described the protoplasm of living 

 follicle cells of the egg of Ascidia canina as having a 

 beautiful reticular structure, and was also able to see that 

 the most external meshes, as well as those round the 

 nucleus, had a radial arrangement. He regarded the struc- 

 ture as a breaking up of the protoplasm into " vesicles." I 

 estimate the diameter of the alveoli figured at about 2 yu,, for 

 which reason it is probable, even if not quite certain, that 

 he observed the true protoplasmic structure. 



In 1873 I described the flat epidermic cells of the 

 Pilidium as having a fine net-like structure in surface 

 view ; the study of the optical section showed that this 

 depended on a finely-chambered or alveolar structure of the 

 protoplasm. Although more accurate measurements of the 

 structural relations were unfortunately not made, never- 

 theless I am of opinion that this was not the real minute 

 structure of the protoplasm, but a coarser one produced by 

 vacuolisation. 



In proceeding to criticise briefly the important works 

 published by J. Heitzmann in 1873 upon the structure of 

 the protoplasm and the cell in fact, of the whole organism 

 I find myself in rather a difficult position. For if one 

 takes into consideration the degree of perfection which had 

 been attained by optical apparatus at the commencement of 

 the year 1870, and further, the great difficulties presented 

 by the very objects, namely, small Amoebae, which Heitz- 

 mann made the basis of his views upon the structure of proto- 

 plasm, it is difficult to overcome a certain amount of doubt 

 which arises with reference to his observations. Heitzmann 

 found a reticular framework in the protoplasm of small 



