CERIANTHARIA. 



6l 



tlie apex of the ridge broaden out, so that they come to cover the whole side of the mesogloea facing 

 the centre of the body. In the thick ectoderm which covers these layers as well as the sides of the 

 ridges are found the thin-walled nematocysts, spirocysts, which are characteristic of the median streak 

 as contrasted with the cnido-glandular tract, and also homogeneous mucus and more sparsely granular 



jrti 



Textfigure 8. 



s ms s 



kd 



Textfigure 10. 



Textfigure 8 10. Section of the ciliated tract region of the filaments some way below the stomatodaeum. Fig. 8 of Arach- 

 nactis albida (Type i), Fig. 9 of Cerianthw llaydii (Type 2) and Fig. 10 of Botrucnidifcr norvegicus (Type 3). 



gland cells together with covering cells. The gland cells and spirocysts however are not uniformly 

 distributed over the above surface. For, as far as I have been able to discover, these cells in all the 

 species examined by me except Bolrucnidifcr norvegicus are aggregated at some distance from the 

 stomatodaeum into two groups, forming two streaks one on either side of the mid-plane of the 

 mesentery, whilst the great mass of the covering cells lie in the mid-plane of the mesentery. This 

 arrangement is seen most clearly in Arachnactis lobiancoi, as the median streak is here subdivided 



