Explanation of Plate I. 



Fig. i. Halcurias filatus from Station No. 64. About natural size. 



Fig. 2. Longitudinal section through the upper part of the column of 

 Halcurias pit 'at us, showing the absence of a sphincter muscle. 



Fig. 3. Transverse section through a portion of the column of Halcurias 

 pilafus in the stomatodaeal region. D = directive mesenteries; 

 si = siphonogljphs. 



Fig. 4. Transverse section of the sphincter muscle of Bolocer a pollens. 



Fig. 5. Longitudinal section through the basal portion of a tentacle of 

 Bolocera pollens, to show the tentacular sphincter. 



Fig. 6. Transverse section through the sphincter of Adamsia tricolor, to 

 show its general form. 



Fig. 7. Transverse section through a pair of mesenteries of the first cycle 

 of Adamsia tricolor in the stomatodaeal region. 



