3i6 



DISCOVERY REPORTS 



a considerable extent. The interest of this situation of the organs of Pesta will be dis- 

 cussed later (p. 371). 



Examination of sections of the individual tubules shows that they are composed of 

 columnar cells arranged in well-defined histological groups. In Fig. 3 is seen an oblique 

 section through a tubule, enlarged from the section seen in Fig. 2 (see also Plate XXIV, 

 figs. 2, 4). The obliquity of the section approximates almost to the longitudinal axis of 

 the tubule, the structure of which is therefore clearly seen in both dorsal and ventral 

 regions. 



ext.m. 



Fig. 2. Transverse section through the cephalothorax of Serges tes corniculum at the level of the antero- 

 lateral liver photophores. Fixed Duboscq, Mallory's triple stain, x 52. ale. alimentary canal; branch. 

 branchiostegite ; dig.l. digestive portion of the liver; e.xt.m. longitudinal extensor muscle ;/?c.v.w. longitudinal 

 flexor muscle; lum.l. tubules of the luminous portion of the liver; n.comm. commissure of the ventral nerve 

 cord ; r.hr.ch. roof of the branchial chamber. 



Ventrally the cells forming the blind tip of the tubule (Fig. 3, I.e.) are not remarkable. 

 Their cytoplasm, at any rate after the fixative employed, is homogeneous, there being 

 no inclusions or intracellular structures other than the nucleus, which is situated basally, 

 that is, remote from the lumen of the tubule. The nucleus is about 10 /< in its greatest 

 dimension, and has its chromatin fairly regularly arranged upon the linin meshwork. 

 These ventral cells are smallest at the tip of the tubule, are sharply differentiated from 

 the cells above them, and form a more or less homogeneous double concave lens-like 

 cap at the distal end of the tubule. It is highly probable that if the tubules prove to be 

 luminous this cap plays the part of a condenser in concentrating the light rays. 



