324 



DISCOVERY REPORTS 



md.b. 



md.org: 



character (Figs. 7, 8, phot.c.) which I beUeve are the photogenic cells. In Fig. 7 a 



tubule is clearly seen on the lower left side of the mandibular organ {hm.l.), but is cut 



across very obliquely, so that the plane of section 



passes through its tip and then through the wall 



of the opposite side some distance above it. It 



therefore shows the two zones of cells composing 



the tubule. Other tubules in the figure are less 



clearly defined owing to crowding and the plane 



of sectioning not being appropriate. 



Before describing in greater detail the charac- 

 teristics of the cells composing a modified tubule, 

 attention may be drawn to its lumen. As already 

 mentioned, this is stellate in cross-section in the 

 normal liver, but it becomes circular and narrow 

 in the denser region of the luminous tubule, 

 expanding again but remaining circular at the 

 extreme tip where it is bounded by the sup- 

 posed photogenic cells. 



Fig. 8 shows part of the tubule referred to in 

 Fig. 7 illustrated in greater detail. The cyto- 

 plasm of the cells forming the greater part of 

 the wall of the tubule (l.c.n.v.) has an irregular 

 granulated appearance, and stains uniformly 

 with the counterstain employed. No vacuoles J'^" t' .T''"^'^!" oi Parapauddus richardi, 



. '^ ■' detached trom the body, with the mandib- 



or other mtracellular structures were observed, ^lar" luminous organ (modified liver tubules) 

 The nuclei of these cells are well represented adhering to its base, x 33 approx. md.b. base 



by that indicated as U. l.c.n.v., being usually °f *^^ mandible; md.org. mandibular organ. 

 , • 1 ^11- 1 The arrow indicates the level of the section 



spherical or ovate and showmg a central mass • pj 

 of chromatin with smaller peripherally deposited 



masses. The central mass appears partially to obscure a nucleolus. The cells enclosing the 

 tip of the tubule, on the other hand, are in distinct contrast to those just described. They 

 are slender and arranged radially in a regular manner, with their rounded and tapered 

 ends projecting into the lumen. Their cytoplasm is of almost uniform density throughout 

 the cell, being perhaps a little denser basally and in some cases along the edge contiguous 

 with the neighbouring cell. Use of an oil-immersion objective shows the presence of 

 delicate longitudinal striae or fibrils, visible more by reason of a slightly different refractive 

 index than by any staining characteristic. These striae are shown in the photogenic cells 

 in Fig. 8, where they are somewhat emphasized. The nuclei of the cells of the tubule tip 

 are entirely characteristic. They are ovate or in many instances kidney-shaped, with a 

 conspicuous chromatin knot lying at one side. From this knot, in which the nucleolus 

 may often be seen, the remainder of the chromatin spreads as a radiating reticulation. 

 The orientation of the nuclei with respect to the position of the tubule tip is constant, 



