34 



bulletin: museum of comparative zoology. 



The posterior portion of the proboscis is comparatively thin and 

 is destitute of papillae. Here only a viscid mucus is secreted. 



The epithelial lining of the proboscis is continuous with that of 

 the rhynchodaeum and like the latter is ectodermic in origin. The 

 musculature is derived from the mesoderm, and in most cases is 

 attached on all sides to the tissues of the head in the brain region. 

 In Carixomella, however, the longitudinal muscles arise from two 

 thick strands (PI. 6, fig. 54, emp.) which are inserted in the tissues 

 of the head immediately anterior to the brain. 



B. Hoplonemertea. — In this order the proboscis is more 

 highly specialized than in the other orders, and is (except in 



(TCTlt 





lep 



-a 



^ ^^hm 



Fig. \(>.— Amphiporus bimaculatus. Transverse section of proboscis, showing 

 sharply defined proboscis nerves (pn) ; a, fibrous dissepiments passing tlirough 

 longitudinal {Ini and Im') and inner circular (icm) muscles. 



Pelagonemertes) 2:)rovided with a highly developed armature, 

 consisting of one or more acutely pointed central stylets and 

 (except in Carcinonemertes) with at least two pouches of acces- 

 sory stylets. 



The proboscis is made up of three chambers. The most anterior 

 of these is lined with highly columnar, glandular epithelium, which 

 is thrown up into prominent papillae. This chamber constitutes 

 by far the major portion of the proboscis and is followed by a short, 

 bulb-like middle chamber lined with a single layer of columnar cells. 

 The posterior chamber is slender, lined with glandular columnar 

 epithelium which secretes a viscid mucus, but which is not thrown 

 up into papillae. 



