CERIANTHARIA. 



6i 



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

 the centre of the bod>-. In the thick ectoderm which covers these layers as well as the sides of the 

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

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



ml 





^MmlffiJ^. 





lid 



Textfigure S. 



Textfigure 9. 



s , ms 



g|?^|%^ hdVt^ c£;^:|6 



cfe'*': 



Textfigure 10. 



Textfigure 8 — 10. Sectiou of the ciliated tract regiou of the filaments some waj- below the stomatodaeuni. Fig. 8 of Arach- 



nactis albii/a (Type l), Fig. g of Orianllius llovilii (Type 2) and Fig. 10 of Botrucnidiffr norvcgicus (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 Botrucnidifcr norvcgictts are aggregated at some distance from the 

 stomatodaeuni 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 seeu most clearly in Arachiiactis lobiaiicoi, as the median streak is here subdivided 



