'53 



EXPLANATION OF PLATES I-IV. 



All the figures refer to Flahelhuii riihruni unless otherwise 

 stated, ect. Ectoderm, c. ect. Calicoblast ectoderm, end. Endo- 

 derm. s. I. Structureless lamella, n. I. Nervous layer of the 

 ectoderm. /. n. Tentacular nematocysts. oid. n. Reduced 

 endodermal nematocysts. in. g. c. Mucous gland cells. 

 g, g. c. Granular gland cells, f. b. Ingested foreign bodies. 

 f. g. Fat globules, m. f. Muscular fibres. 



Fig. I. Section of the calicoblastic ectoderm on the side of 

 a septum about i mm. inside the edge against the axial fossa. 



Fig. 2. Section of the attachment of the body- wall to the 

 corallum at the base of a mesentery. 



Fig. 3. Section of the body- wall over a septum near its 

 upper free edge. 



Fig. 4. Section of the ectoderm of the external body-wall. 

 (The section is that of a knob caused by the contraction of 

 the polyp. It serves to show the constituents of the layer, 

 but does not give in any way a real idea of its true appear- 

 ance. It was chosen only alter a prolonged search, no other 

 section in this position showing more than i nerve cell and 2 

 or 3 granular gland cells. The vacuolated nature of the 

 layer does not appear). 



Fig. 5. Section through a battery of nematocysts on a 

 partially retracted tentacle. 



Pig. 6. Section through the ectoderm of the stomodoeal 

 wall over the attachment of a mesentery. 



Fig. 7. Section of the stomodoeal wall between the attach- 

 ments of two mesenteries. 



Fig. 8. Transverse section of the mesenterial filament and 

 edge of a primary mesentery at about the middle of its course. 

 (For the sake of clearness no tone has been placed over the 

 structureless lamella). 



Fig. 9. Reduced endodermal nematocyst, reconstructed 

 from a series of sections. 



Figs. 10-15. Various stages in the development of the 

 corallite. The numerals where present refer to the cycles of 

 the septa. 



Fig. 16. Scar of a broken-off corallite. The dark lines in 

 the septa are depressions, due to the eating away of the 

 corallum along the central '' dark lines "' of the septa. 



