part 3] 



THE KELESTOMIX-E 



209 



(fig. 5). The last condition is never attained by the Kelesto- 

 minae; but both Kelestoma and Morphasmopora have abundant 

 interoecial secondary tissue with elongate lacuna?, and, in Mor- 

 phasmopora Jukes-brownei, these elongate lacuna?, whether in the 

 form of long slots or very much lengthened triangles, take on 

 a curved or wavy shape, and often simulate the apertures of 

 avicularia. 



Fig. 4. — Diagram representing a 

 further development of the 



condition, represented in fig. 3. 

 The secondary tissue (black) 

 has increased in amount. 



Fig. 5. — Diagram .showing a still 

 further development of secon- 

 dary tissue (black) which now 

 completely fills the interoecial 



rat tegs, and has no median 

 lacunae. 



The behaviour of the Kelestomine avicularia also is noteworthy. 

 We have seen that the sporadically-distributed, indifferently- 

 orientated, blunt-apertured avicularia of the Primitive Pelma- 

 toporid became the definitely-placed and definitely-orientated, 

 somewhat acute-apertured avicularia of the Primitive Kelesto- 

 mine. The numbers are fixed at four, in two pairs, in connexion 

 with the aperture of every normal cecium; and, of these pairs, the 

 more proximal is placed in the interoecial tissue just beside the 

 proximal pair of apertural spines, and the distal pair just distal 

 to them. During evolution, the proximal pair are sooner or later 

 discarded, and the distal pair become raised on long pillar-like 

 pedestals that keep at about the same height as the fusion of the 

 proximal apertural spines with the fused distal forks of the aper- 

 tural bar, and form with them the proximal shield of the secondary 



