26 H. V. NEAL 



connections of neural tube and myotome and he reached the 

 same conclusion as did Dohrn ('88), namely, that they are 

 secondary in origin and that they arise by the extrusion of 

 processes of medullary cells which Neal regards as neuroblasts. 

 Froriep ('04) stated with equal positiveness that the protoplas- 

 mic bridges are connected with intramedullary cells. Against 

 the assertions of these three observers we have the statement 

 of Paton that ''probably the long processes depicted by this 

 investigator as being projected from medullary cells are in real- 

 ity made up of two components: a short process and the long 

 undifferentiated protoplasmic strand or bridge with which it is 

 apparently fused so as to give, in specimens stained by certain 

 methods, the appearance of a single long process." 



This assertion taken in connection with Paton's criticism 

 (quoted above) of my results as based upon inadequate methods 

 of preservation and staining suggests the possibility that Paton 

 himself has been unable to reach positive conclusions regarding 

 the histogenesis of the 'protoplasmic bridges' and the relations 

 of theii* cellular components because of too implicit reliance upon 

 a method primarily suited to demonstrate the neuro-fibrillae 

 but quite unsatisfactory for general cytological purposes. How- 

 ever adequate — or inadequate — the Bielchowsky-Paton method 

 for demonstrating the histogenesis of the neuro-fibrillae, it ap- 

 pears quite unsuited for demonstrating the cellular boundaries 

 and relations. For this purpose, the vom Rath method as used 

 by Neal ('03) is superior. The difference between the cytologi- 

 cal results obtained by the Paton method and those obtained by 

 the vom Rath method are strikingly shown by .a comparison of 

 Paton's figure 2, plate 23, and figure 11 of the present paper, 

 which represent almost exactly identical stages in the histogen- 

 esis of somatic motor nerves. The most striking difference con- 

 sists in the absence of cell boundaries in the former and in their 

 clear definition in the latter. (See fig. A, p. 25.) 



But Paton's failure to determine the histogenesis of the 'pro- 

 toplasmic bridges' is not wholly due to his failure to use a method 

 of fixing and staining which demonstrates cell boundaries and 

 relations, l)ut there is evidence also that he did not make a 



