âO CHAELES F. W. MCCLURE, 



treat of the histology of the nerve cells of Invertebrates. Among 

 these may be mentioned the investigations of Rawiz, Nansen, Rohde, 

 Haller, Binet, de Nabias, Pflücke and Lugaro. The paper by 

 Rawitz (31) deals chiefly with the histology of the nerve cells of 

 mussels, which he studied by the isolation method as well as by 

 sections. The ordinary indifferent fluids were used for the isolation 

 method, while the picro-sulphuric solution of Kleinenberg gave the 

 best results for the study of sections. His general results as to the 

 cell structure may best be summed up in his own words p. 403 : "Wir 

 ersehen also aus diesen Beobachtungen, dass die Ganglienzelle der 

 Acephalen aus zwei Theilen besteht, von denen der eine eine netzförmig 

 angeordnete, der andere eine zähe, unter Umständen ölartige Tropfen 

 bildende Substanz ist, die in den Maschenräumen der erstem suspen- 

 dirt ist." 



He suggests the possibility that these drops may alone constitute 

 the true functional nervous element in the cell, while the network 

 serves simply as a support for the former. 



Nerve cells that had been macerated in weak solutions of alcohol, 

 or potassium bichromate, presented a structure which differed materi- 

 ally from that mentioned above. Here they appeared to be finely 

 granular in structure, and a division of their constituent elements 

 into two chemically and morphologically different substances, was not 

 to be made out. He accounts for this in the following manner p. 404 : 

 "Es würde dann das zart granulirte Aussehen der Zellen verursacht 

 durch die in der netzförmigen suspendirte zähe, tropfenbildende Sub- 

 stanz, in deren Innerm Gerinnungen durch die coagulirende Wirkung 

 der Reagentien entstanden sind." 



In only one instance (fig. 32) does he figure the presence of 

 fibrils in these cells. 



Nansen's investigations (25 and 26), upon the finer structure of 

 the nervous system of Invertebrates, cover a wide range of forms^ 

 including species of Mollusca, Vermes, Crustacea and Tunicata. His 

 conception of the finer structure of the nerve cells of Invertebrates 

 may be summed up as follows. 



The contents of the axis-cylinder processes consist of primitive 

 tubes which he says "are extremely slender tubes or cylinders, sepa- 

 rated from each other, or rather formed by membranes or sheaths of 

 a firm supporting substance, spongioplasm, very much resembling 

 the neuroglia-substance". The viscous contents of these primitive 

 tubes, the hyaloplasm, he regards as the true nervous substance. 



