STROPHOMENIA AGASSIZI. 231 



these folds unite posteriorly and bound the cirri, relatively thick, finger-shaped 

 processes that appear, with very few exceptions, to be attached separately to 

 the atrial wall. 



What is probably the true mouth opening occurs in the postero-lateral 

 atrial wall and leads into the long pharynx characteristic of Strophomenia. 

 At the outset the walls of the pharyngeal tube are relatively thin, numerous 

 radial muscles attach it to the body wall, its epithelial lining is developed into 

 many low folds and a very few gland cells are scattered over its surface. Passing 

 backward one third of its length it will be found that the radial muscles dis- 

 appear, the circular and longitudinal muscles become more abundant, the 

 tube grows more circular and multitudes of pyriform gland cells, arranged in 

 lobules, appear upon its outer surface. This state of affairs continues to the 

 stomach-intestine. 



A radula is present, but it is of small size and stains so faintly that even 

 under high magnification it is difficult to interpret its true form. It contains 

 a small number of transverse rows, appears to belong to the distichous type, 

 and in one section there are evidences that each tooth is comb-like with five 

 sharply pointed cusps. 



As in other members of the genus there are two, long tubular ventral sali- 

 vary glands opening on each side of the radula into a shallow depression in the 

 pharyngeal wall. Each of these organs consists of two divisions (a) a slender 

 duct leading from the pharynx to the distal end of the gland where it ends 

 blindly, and with the exception of a small division in close proximity to its 

 outlet this canal is covered by (b) a sheath of gland cells which probably pour 

 their secretion through intercellular channels into the central canal. 



While the transition from the pharyngeal epithelium to that of the stomach- 

 intestine is abrupt the muscular coat about the pharynx passes for a consider- 

 able distance over the ventral surface of the stomach-intestine proper and the 

 anterior intestinal coecum. This last named organ is highly developed, pos- 

 sesses digestive cells and lateral pouches like those of the succeeding sections 

 of the gut and extends anteriorly as far as the forward border of the atrium. 

 Throughout the body the character of the mid-gut is constant, the pouches 

 especially being remarkably regular. Ventral to the gonad the digestive cells 

 are replaced by low, cubical ciliated elements that beneath the pericardium form 

 an extensive tract. As the gut narrows this tract grows circular as it forces its 

 way between the halves of the shell gland and the ciliated elements approach the 

 mid-ventral fine of the gut to become the only lining of the rectum. Near its 



