76 



CERIANTHARIA. 



found aggregated at the aboral end of the ciliated tract region, forming bunches. These bunches 

 answer to the wavy coils of the cnido-glandular tract. 



2) Craspedonemes which possess only an ascending limb of the filament (Textfig. 13). This 

 is the case in P. maua. Here evidently the filament has not yet reached the aboral side of the cras- 

 pedoneme in the course of its growth. 



The cnido-glandular tract more rarely forms a craspedoneme and only on mesenteries 

 whose cnido-glandular tract region is extremely slight. This is so with certain mesenteries of Pachy- 

 cerianthus solitarius (Textfig. 14) and sometimes in Ccrianthus lloydii. Still the wavy coils of the 

 cnido-glandular tract correspond, as already mentioned, to the bunches in the ciliated tract, though 

 they may not display such thread-like formations as the ciliated tract, but even so the cnido-glan- 

 dular tract traverses processes of mesenterial entoderm and mesogloea. 



The craspedonemes of the craspedion region are met with partly in the form of acontia 

 partly in the form of craspedonemes imdifferentiated in outward appearance. 



The "acontia" are rounded in transverse section. The filamentous part consists mainly of 

 mucus cells: they are provided with an ectodermal muscle layer. In the endoderm numerous nema- 

 tocysts may sometimes (often?) be developed. Typical "acontia" are found in Araclu/antliits and in 

 Arachnactis albida (Textfigure 15). 



The more undif ferentiated craspedonemes of the craspedion region retain partially the 

 mucus cells and spirocysts, but have developed in addition granular gland cells and thick-walled 

 nematocysts. Such craspedonemes have hitherto been met with only in Ccrianthcopsis amcricanns 

 (Textfigure 16). 



Finally, as modified craspedonemes of the craspedion region may be regarded the Botru- 

 cnidae. Typical botrucnidae are found in Botrucnidifcr norvcgicits and in many of van Beneden's 

 Ceriantharia-larval forms (Textfigure n). 



