Montgomery, Central Netvotis System of Nemeiteans. 207 



I, 2, 3 and 4. Of these the 4th type, or neurochord cells, are 

 present only in Cerebrattiliis. All these cells are membraneless, 

 and in all the cytoplasm has a remarkable vacuolar structure, — 

 strands of spongioplasm bounding large hyaloplasmic vacuoles. 

 Such a remarkably vacuolar structure does not appear to be 

 normal in any other group of animals. In cells 3 of Lmeiis 

 occur in the cytoplasm peculiar homogeneous, rounded bodies, 

 which have no regular arrangement, and which are not compar- 

 parable to the chromophilic granules (Nissl's granules) of other 

 forms : for them the term chromopJiilic corpuscles was employed ; 

 genetically they seem to be local condensations of the cyto- 

 plasm. A large number of fixing reagents were employed, but 

 after them all the axis cylinder process (I was unable to find the 

 dendritic processes described by Burger) presented the appear- 

 ance of a single nerve tubule, and did not contain any primitive 

 fibrils ; that is to say, the outer (alveolar) spongioplasmic sheath 

 of the cell body is continued distad to form the outer sheath of 

 the axis cylinder, and the hyaloplasmic, structureless substance 

 to form its core. Spongioplasmic strands may penetrate a short 

 distance into the proximal end of the cell process, but this is 

 an irregulur phenomenon, and such strands are not prolonged 

 to form fibrils. Thus the minute clear spaces in the fibrous 

 core of the central nervous system represent axis cylinders, 

 and bundles of such ; and the larger and more irregular clear 

 spaces, lymphatic tracts. 



In the brain lobes and the lateral nerve chords the follow- 

 ing connective tissue layers may be distinguished : the outer 

 neurilemma, which is a capsule enveloping the ganglion cell 

 layer ; the inner neurilemma, a capsule separating these cells 

 from the fibrous core (" dotted substance "). This tissue is the 

 same as that forming the connective tissue basement membranes 

 of all the epithelia of the body, and is formed of branching 

 cells with a dense intercellular substance (cf. Montgomery, 

 Spengel's " Zool. Jahrb." 10, 1897). A different tissue forms 

 the neuroglia proper (" Hullgewebe," Burger). This neuroglia 

 consists of branching cells, without any intercellular substance. 

 Within the ganglion cell layer its elements envelope with their 



