Anatomy <i)id Ilistologij of a New EartJiiconn. Go 



sections the appearance of cross striation. In the small fibers 

 they seem to form a single continuous series, the individual 

 fibril being wider or narrower according to the part of the fiber 

 it occupies. But in large fibers the fibrils reach across the 

 shorter diameter only at the ends of the series, and medially 

 form two series, one at each edge, with a central space between 

 them, as if fibrils of a single series had been broken at the 

 middle and the two series thus formed were slightly parted. 

 Upon tearing apart the elements of stained fibers an inter- 

 stitial granular protoplasm becomes apparent, adhering to the 

 surfaces of fibrils in shreds and deeply-stained knots. 



Longitudinal vertical sections of the brain show the latter 

 to be slightly depressed at the sides, where the sections are ellip- 

 tical in contour. Medially the brain is less flattened. The 

 fibrillar central tissue is surrounded everywhere, except 

 anteriorly and along the ventral middle line, by numerous 

 rather small unipolar nerve cells of the usual structure. 

 Certain of the anterior cells, above and below, are larger than 

 the others and occupy a depression in the fibrillar substance. 

 The nervous tissue is invested and protected by fibrous con- 

 nective tissue, the nuclei of which are scattered among the 

 nerve cells and occur between the divisions of the fibrillar 

 nervous matter. Outside this investing material is a moderately 

 thick sheath, in which may be distinguished numerous blood 

 vessels, connective tissue, and a highly refracting granular 

 material, the nature of which has not been determined. Upon 

 the posterior surfaces, dorsal and ventral, the bands of muscle 

 referred to in another part of this paper can be seen, the larger 

 bands consisting of about three fibers. Excepting these bands 

 there seems to be no muscular tissue in the brain sheath. The 

 sheath covering the dorsal side of the brain has a very sharply- 

 defined inner boundary consisting of a membrane, apparently 

 of homogeneous matter and probably a modified connective 

 tissue. There is some appearance of such a membrane at the 

 ventral side, but it is here much less distinct. The outer limits 

 of the sheath are not well defined. The commissures between 

 the cerebral and sub-oesophageal ganglia are enclosed in a thin 

 sheath, in which may be seen the same refracting granules as 

 are found in the brain sheath. No muscular tissue is present, 

 apparently. 



