I^.-) s. GOTO. 



would lie ill (liui^'er of l)eiiig swept away. Ijiif on tliis head nothing 

 (U'fiiiitc c;in l)e asserted. On tlie other hand, tlie coinjtanitively 

 l^erfect structure of the eye in 7V. viohif may l)e due to tlie hal)it of 

 tliis species. For, according to Lang" and ]\[onticelli-' this 

 worm is met witli very commonly on the surface of the body of 

 <Jrt]i(i<ifiris('iis inohh and is thus constantly exposed to light, wliich is 

 not the case in 7V, orale. 



In cross-sections the l)rain as well as the nerves show the re- 

 ticulated a})])e:u'ancc so universallv described by students of tlie flat- 

 worms. In the brain of 'J'risloiiiiuii. the meshes are completely 

 tilled with nervous libi-es, direct continuations of the ])rocesses 

 of ganglionic cells (PI. X.XIII, tig. 4; IM. XXIV, fig. 12; PI. 

 XX \", fig. 7 ; PL XXI, tig. 1); but in the nerves tlie libres often do 

 not quite fdl up tlie meslies, but leave a cleai* sjtar-e Ix'tween them- 

 selves and the walls of the meshes. In TriMomnm^ as has already been 

 mentioned, the fibres show less and less an affinity for stains as we 

 recede from the nucleus, and finally they can scarcely be distinguished 

 from the fluid tliat fills the meshes of the connective tissue ; so that 

 in this case the meshes of the nerves are seen in cross-section to be 

 mereh^ filled with a very weakly staining, slightly granular substance 

 (PI. XX, fig. 10). In Viclidoplioni the nervous fibres are very 

 slender, and in cross-sections are seen merely as minute dots (PI. XI, 

 fig. 1) ; while in neiu-ly all other species the nervous fil)res are very 

 difficult to make out in cross-sections. The nerve itself, however, can 

 be followed with certainty for the greater part of its course, but 1)ecomes 

 indistincl in the posterior part of the body where, as already stated, the 

 mesenchvma consists almost exclusivelv of reticulated connective tissue. 



1). Laug—/, c. p. 29. 



2). Monticelli — Intorao ad alcuni ehniuti del Museo Zoologico delli K. Univorsità di 

 Palermo. Xatiiralista Siciliauo, An. XTI, 1893. Estratto p. 5. 



