146 



/■///•; AMERICAN NA TURALIST. [Vol. XXXVIII. 



of being thick, it is very thin, with large flattened nuclei. In 

 both longitudinal and transverse sections, where a nuclear stain 

 has been used, the epithelium may be readily traced within the 

 cylinders, even to the finer branches. It is exactly similar in 

 appearance to that in the dorsal layer, and is wholly distinct 

 from the cellular elements of the cylinder. Small flat nuclei 

 are seen closely apjilied to the trachece, while the irregular 

 nuclei ot the cylinder cells lie at a little distance away. 



1p, his stud\ ot I.uciola 111 1886, Wielowiejski did not find the 

 cylinder a syncytium, as 

 ^ -v^ stated by Emery, but 



believed it to be composed 

 of two elements, a nucleated 

 epithelium immediately sur- 

 rounding the trachea, and an 

 outer layer belonging to the 

 parenchyma. The latter he 

 ^ ^ found generally separated 



from the trachea by the 



1 .... i„ -scctu.n transverse tn cyhnde,. Her- aCtloU of reagCUtS, but Still 



connected with the paren- 

 chyma cells. These ()bser\ations w^ould seem to be in agree- 



The bulk ot the cylinder is thus shown not to be of tracheal 

 origin. The trachcce pass into the cylinder cefls, there dividmg 



lologous with those of the 

 :aterpillar. If the cylinders 

 at least clearly distinguished 

 tn.m It by (lefinite b()undary lines. Jn some p^^W. 



between the cells of the dorsal layer and those 

 ot the cylinder, but the cylinder cells are much 

 Mualler than those of either the dorsal layer 

 or the parenchyma. They retain their spherical 

 .shape nuich more than either of the others 

 mentioned. It would seem probable that all 



to form the tracheoles, so t 

 ecjually befitting here, altho 



