242 C. M. CHILD. 



Abpral to the cesophagus the inner margins of the mesenteries 

 hane free in the enteron and bear the mesenterial filaments. A 



o 



single pair of very short mesenteries at that end of the mouth 

 where the siphonoglyph is situated are known as the directives. 

 The next mesentery on each side of these extends almost to the 

 aboral end of the body. From this point to right and left the 

 mesenteries decrease in length, following a definite, rather com- 

 plex law which need not be discussed here. On the side oppo- 

 site the directives, at the opposite angle of the mouth are the 

 shortest mesenteries, with the exception of the directives ; these 

 do not extend far aboral to the oesophagus. It is in this region 

 that all new mesenteries are added, /. e., the region of growth is 

 opposite the directives. Thus, proceeding from the directives to 

 the right and left around the body the mesenteries are succes- 

 sively younger. Each pair of new mesenteries appears between 

 the members of the last preceding pair formed, thus separating 

 them. Corresponding to the formation of new intermesenterial 

 chambers new tentacles appear in this region. It is usually pos- 

 sible to find at this point in the normal animal one or two pairs 

 of tentacles much smaller than the others and in process of 

 growth. Corresponding to the number and arrangement of the 

 mesenteries there is one unpaired marginal tentacle over the 

 chamber between the directive mesenteries and known as the 

 directive tentacle. It is usually somewhat thicker than the other 

 tentacles since the space between the directives is greater than 

 that between other mesenteries. The other tentacles are paired 

 right and left. 



In Ccrianthns solitarius the greater number of the mesenteries 

 about the whole circumference of the body do not extend 

 aborally far beyond the cesophagus. Only certain mesenteries 

 extend further, to end at various levels according to their posi- 

 tion. This is also true of Cerianthus lucmbninaccits. 



The muscles of the body-wall consist of a heavy layer of 

 powerful longitudinal muscles which decreases slightly in thick- 

 ness toward the aboral end. These are the chief muscles of the 

 body, circular muscles being absent, and tentacles, disc and 

 cesophagus possessing only a slight muscular development. 



As is well known, the Cerianthidae are found imbedded in the 



