SENSORY EPITHELIUM OF MICROSTOMA CAUDATIM . 55 



With a fine knife, made from a flattened needle, the ciliated pit 

 was cut from either side of the animal. When the right pit was 

 removed the specimen moved about in a spiral path keeping the 

 remaining or left ciliated pit directed towards the center of the 

 spiral path. When the right pit was left intact and the left 

 destroyed the spiral movement was in the opposite direction. 

 Thus the bilateral disposition of the ciliated pits of Microstoma 

 serves the purpose of orienting or directing the Microstoma in its 

 course through the water. 



Again both pits were removed. In such cases it sometimes 

 happened that the cut was a clean one, leaving the specimen 

 divided into a minute, anterior part bearing the ciliated pits and 

 a large, posterior part lacking the ciliated pits and the "brain." 

 In such a case the minute portion moved in a highly active 

 manner, tumbling about in all directions, w r hile the large portion 

 moved slowly in a direct line, except that a w r ide arc to the right 

 or left was occasionally made. This direct course was continued 

 until some inert object was encountered. Such contact would 

 cause a change in the path of the specimen. This large part dis- 

 played no exploratory movements. So it is further suggested 

 that the exploratory movements of Microstoma depend upon the 

 ciliated pits being in a functional condition. 



SUMMARY. 



1. There is present in the mid-ventral floor of the pharynx of 

 Microstoma caudatum Ldy. a sensory epithelium, free from gland- 

 ducts, which lies directly in contact with the posterior, transverse 

 nerve commissure. The manner in which the pharynx behaves 

 in testing food suggests that this is an elementary gustatory 

 epithelium. 



2. The ciliated pit has a glandular and a sensory region. Thus 

 it resembles the "cerebral organs" of the Protonemertini and 

 strengthens the affinity between the Rhabdocceles and the 

 Nemertini. 



3. Microstoma caudatum, Ldy. living in its normal medium tests 

 the surrounding water, etc., with its pharynx and ciliated pits. 

 This testing is facilitated by making numerous exploratory move- 

 ments with its anterior end. 



