﻿Plate 20 

 Siphonosoma ingens (Fisher) 



1, Head of small specimen (Elkhorn Slough, Monterey Bay, Calif.) drawn from 



life; X 8. 



2, Anterior end of paratype, X 1, showing the introvert partly invaginated and 



retractors in contracted state. 



3, Portion of 2 enlarged; X 2. The left root (S *) of spindle muscle has been 



severed. 



4, Nephrostome of a specimen from Newport Bay and associated coelomic 



papillae; X 10. 



5, Coelomic papilla; X 30. 



6, Brain of paratype; X 10. 



CP, coelomic papillae (Keferstein bodies); CV, dorsal contractile vessel; F, 

 fixing muscle; I, introvert; A^, nephridium; NC, nerve cord; A'^O, position of 

 nuchal organ at anterior end of dorsal double series of tentacular lappets; 

 O, esophagus; RD, dorsal retractors; RV, ventral retractors; S, spindle 

 muscle; S', S", lateral roots of spindle muscle; W, wing muscle of rectum. 



Plate 21 



Siphonoso7na ingens (Fisher), types 



1, 2, Anterior half of body; X 1.5. The top of figure 2 is a continuation of the 

 bottom of figure 1. This specimen is unusually well relaxed. The 

 coelomic papillae have been omitted and the muscle bands are only 

 slightly indicated in order to avoid confusion of lines. 



3, Same specimens; X 3. Point where the esophagus joins and is fastened to 



the ascending intestine at beginning of rectum, showing relations to 

 spindle muscle (S) and its lateral roots, S', S" ; the fixing muscle to 

 esophagus is omitted. 



4, A segment of the esophagus and four retractors opposite the wing muscles 



of rectum to show the lateral mesenteries of esophagus; X 5. M, right 

 mesentery. Other lettering as for plate 20. 



442 



