% 



HISTOLOGY OF ASTRAEIDS 121 



section through a tentacle showing a sub-terminal battery. Since the 

 section was cut somewhat obliquely, the middle lamina and its specialized 

 longitudinal fibres (Ig.f.) appear thicker. 



Fig. 4. — Larva of I'"'avia fragum (Esp.) ten hours after extrusion. 

 Part of transverse section through column- wall. Note fibrous condition 

 of middle lamina ami protoplasmic remains in coelenteric cavity. 



Fig. 5. — Coeloria daedalea (Ell. and 8ol.). Part of transverse 

 section (slightly oblique) through stomodaeum, showing a ridge and 

 adjacent intermesenterial areas. 



Fig, 6. — Ibid. Part of transverse section through a principal mesentery 

 just below stomodaeal region, showing contiimation of median groove on 

 filament. 



Fig. 7. — -Ibid. Part of transverse section through a principal mesentery 

 below stomodaeal region, showing straight region of filament and the two 

 endodermal lobes. 



Fig. 8.- — ^Ibid. Part of transverse section through a subsidiary mesentery, 

 showing straight region of filament and the two endodermal lobes. 



Fig. 9.^ — Ibid. Part of transverse section through pleatal region of 

 a principal mesentery in stomodaeal region. 



Fig, 10. — Fa via hululensis (Gard.). Part of transverse section 

 through column-wall at base of polyp. The middle lamina is thin and 

 somewhat discontinuous at this level. 



Fig. 11. — Coeloria daedalea (Ell. and >Sol.). Longitudinal fibres 

 of the middle lamina of a mesentery after maceration in osmic- acetic 

 solution and staining in borax-carmine and jiicro-nigrosin. 



Fig. 12. — Ibid. Part of tangential section (6 n thick) through a mesen- 

 tery, showing the network of branching fibres of the middle lamina. Note 

 the mass of unbranched fibres and nuclei in the middle lamina. 



Figs. 13-15. — Showing stages in the formation of column-wall processes 

 in the calicoblastic layer. 



Fig. 13. — Leptoria gracilis. Part of transverse section through 

 intermesenterial region of column-wall at level of stomodaeum. 



Fig. 14. — Ibid. Part of transverse section through column-wall at 

 attachment of a mesentery in stomodaeal region. 



Fig. 15. — C!oeloria daedalea (Ell. and Sol.). Part of transverse 

 section through column-wall at attachment of a mesentery in stomodaeal 

 region. 



Fig. 16. — Metridium senilis. Part of transverse section through 

 column-wall, showing a ridge. In the middle lamina note (1) the swollen 

 loosely spongy core which is less open towards the ectoderm and endoderm, 

 the network itself consisting of branching fibres ; (2) circularly arranged 

 unbranched fibres bounding the spongy core, the fibres being massed 

 «,gainst the endoderm ; (3) nuclei in the spongy core ; a thin granular 

 protoplasmic area can be seen around most of them. The points marked 



