41 6 MONTGOMERY. [Vol. XIII. 



Fig. 42 a-e, corroborate his former view, and show that the 

 neurochords possess equal dichotomic divisions. 



Though I have followed Burger ('90b) in applying the terms 

 "neurochord cells" and "neurochords" to nemerteans, — 

 terms introduced by Eisig ('87) for the colossal ganglion cells 

 and their fibres in annelids (which structures had been recog- 

 nized first by Leydig, '64, as nerve tubules), — yet I would 

 not intend to express, by the use of similar terms, homologies 

 between these structures in different animal groups. Fried- 

 lander ('89) maintained such a homology in different animal 

 groups, or at least declared the neurochords of different groups 

 to be "fundamentally the same" structures (p. 258). But 

 what is meant by the expression " fundamentally the same," if 

 not homology .'' But though the neurochords may present simi- 

 lar structural relations in the different animal groups (Nejner- 

 tini, Annelida, Arthropoda, Leptocardid), their homology is not 

 thereby proved ; for there is as much probability for the as- 

 sumption that they have been developed independently by 

 these various forms. And notwithstanding the large number 

 of investigations already made upon neurochords,^ it is still 

 necessary to subject them to renewed study, with the aid of 

 the newer histological technique, and to treat them from the 

 comparative standpoint. 



IV. Neuroglia. 



As Burger ('90b) has demonstrated, the brain lobes and lateral 

 chords are compounded of the following layers: (i) the outer 

 neurilemma (Fig. 25, 0. Netir.), a connective-tissue capsule 

 enveloping (2) the ganglion-cell layer, and (3) the inner neuri- 

 lemma (i. Neur.), which separates the latter layer from (4) the 

 central fibrous core (composed of "dotted substance"). Burger 

 had also described the connective-tissue elements of the 

 ganglion-cell layer, and termed it " intracapsulares Bindege- 

 webe " or " Hiillgewebe "; he discovered, also, a layer of cells 

 of this tissue situated between the inner neurilemma and the 



1 A nearly complete bibliographical list of papers dealing with neurochords has 

 been given by Friedlander ('89). 



