152 G 



Canadian Arctic Expedition, 1913-1918 



PLATE XXV. 



Fig. 1. Biddiopsis arctica Verrill. Type. Transverse thick glycerine section across near the 



upper part of the column, showing 12 perfect and eight imperfect mesenteries; 



d, sulcar; d', sulcular directives and siphonoghlyphs; 1, 1, gonads on imperfect 



mesenteries; o, stomodseum. Schematic, in part, 

 la. The same. One of the perfect mesenteries more enlarged. 

 Ib. The same. Conchula and siphonoglyph much enlarged. 

 Ic. The same. Distal part of a tentacle; much enlarged. 



Id, a, b. Sections of two tentacles compressed into angular forms by crowding, 

 le. The same. Longitudinal section, in the region of the sphincter muscle (e); much 



enlarged. 

 If. The same. Portion of a mesenterial filament partly uncoiled. Ig. Another portion 



more enlarged; Ih, trifid portion, 

 li. The same; transverse section at base of the stomodseum, showing the bases of the 



directive mesenteries (d); g, ectoderm; h, mesoglcea; h', lines of circular muscles. 

 li. The same; terminal pore and ends of mesenteries seen from inside; enlarged. 

 Ik. Section of aboral end and pore expanded; m, mesentery; p, pore. 



2. Metridium dianthus (Ellis). A large living specimen with some acontia emitted; 



from Massachusetts Bay; n, n, acontia; about f natural size. 



3. Siphonactinia parasitica. Two of the mesenteries in transverse section. After McMur- 



rich, with some changes. 



Figures 1-lk, were made from rather thick sections mounted in glycerine- jelly and therefore 

 differ from hardened sections in Canada balsam. By the author. Fig. 2, after J. H. Emer- 

 ton, with some changes. 



