On the connective tissues und l)()dy cavities of the Nomerteans. 31 



have the form and structure of those in Amphiporus^ it is especially 

 characteristic for Teirastemnia under the genera examined, that the 

 parenchym cells are more or less unequal in size : thus occasional 

 cells occur, especially on the lateral periphery of the proboscis 

 sheath, which have about 3 to 5 times the diameter of the average 

 cells. 



4) Intracapsular tissue of the central nervous 

 system. This consists of small, membraneless , multipolar cells, 

 the nucleus being usually elongate-oval, though fre(iuently irregular 

 in outline, the chromatin forming a thick peripheral layer, and one 

 or two nucleoli are sometimes present. This tissue is more aliundant 

 than in Stichostetmna, and in its ditferentiation, closely resembles that 

 of Amphiporus glutinosus; we may distinguish three modifications: 



a) Cells in the brain lobes, between the outer and inner neuri- 

 lemma, being situated mainly peripherally from the layer of ganglion 

 cells. These cells contain a yellowish pigment, which is distributed 

 either in the form of exceedingly fine granules, in the cytoplasm and 

 cell fibres; or, more usually, each cell contains a few, large, homo- 

 geneous granules in the proximity of the nucleus, which are probably 

 fused masses of the finer granules. 



b) Cells in the lateral nerve chords, between the outer and inner 

 neurilemma. Similar to the preceding, but without i>igment. 



c) Cells in the brain lobes and lateral chords, within the fibrous 

 core ; they form no peripheral layer around the latter, and occur very 

 sparingly. These cells resemble b), excei)t that their nuclei are smaller, 

 and stain more intensely, 



5) Interstitial connective tissue of the body epi- 

 thelium (Fig. 38). This consists of membraneless, multii)olar cells, 

 with fine branching and anastomosing fibres; the nuclei are spherical, 

 and are smaller, and stain more intensely, than those of the gland- 

 and supporting- cells of the epithelium, between the proximal portions 

 of which cells this connective tissue forms a network. In T. vermi- 

 culum it contains no pigment; the interocular pigment stripes of the 

 head owe their existence' to pigment contained in the supporting 

 cells of the epithelium; but only in this region do the supporting 

 cells contain pigment. 



VIII. Tetrasteftinia catenulatum (Verr.). 

 The histology of the other connective tissues is as in T. vermi- 

 culum, but we find differences in the interstitial connective 



