No. 3-] STUDIES ON THE HETERONEMERTINT 417 



fibrous core. In a paper ('97) on the cytology and compara- 

 tive distribution of the connective-tissue elements in the nemer- 

 X.Q.dSi'&iyCarinella, Cerebrahihts, Lineus, Amphiporus, Tetrasteimna, 

 Stichostemnid), I have given detailed descriptions of the cellular 

 elements forming the neurilemmatic capsules, and the " Hiill- 

 gewebe" (this latter I termed "neuroglia"); forfuUer structural 

 details of these elements, I must refer to the paper in question. 

 Now I agree with Burger's conclusion ('90b, p. 137): "Das 

 Pigment fuhrende Hiillgewebe der Ganglienzellbiindel . . . und 

 der faserig-zellige Mantel des Faserstammes . . . sind urspriing- 

 lich ein und dieselben Gewebsgebilde, ortlich von einander 

 getrennt und differenzirt." But he adds (p. 138): " Sie sind 

 vielleicht als mit dem Neurilemma in Gemeinschaft entstanden 

 zu denken, jetzt aber so sehr von den Bildungen desselben 

 verschieden, dass sie fiir sich zu betrachten sind. So sind sie 

 auch mit der Glia (Hatschek's) unvereinlich, da sie jhrem 

 vornehmsten Kriterium Scheiden- oder Rohrenbildnerinnen 

 niemals entsprechen." I have shown in my previous paper 

 (/. c), however, that the elements of the neuroglia (Burger's 

 " Hiillgewebe ") and those of the neurilemmatic sheaths must 

 be considered as distinct for the following reasons: (i) because 

 the tissue of the neurilemma is identical with the connective 

 tissue forming the basal membranes of all epithelia, with that 

 enveloping the muscle bundles, etc., and consists of branched 

 cells lying within a dense intercellular substance, while the 

 neuroglia is restricted to the nervous system, and its cells are 

 not imbedded in an ectoplastic, intercellular substance; and (2) 

 because no intergradations between these two tissues occur, 

 not even in that primitive form Carinella. Further, as shall 

 be described, the branching fibres of the multipolar neuroglia 

 cells not only produce a loose network around the ganglion cells 

 (III, IV), but also form the outer connective-tissue sheaths of 

 their nerve tubules. Thus Burger's " Hiillgewebe " is a typical 

 neuroglia tissue, and can stand in no histogenetical relationship 

 to the tissue of the neurilemmatic sheaths. It is more prob- 

 able, indeed, in the light of our knowledge of the ependyma 

 (embryonal neuroglia) in vertebrate histogenesis, that the 

 neuroglia of the nemerteans stands in closer genetical relation 



