﻿EXPLANATION OF PLATES 



Plate 18 



Sipunculiis nudus Linnaeus 



1, A portion of the internal structure to demonstrate the extra intestinal spiral 



A, which has been dissociated from the regular spiral B and drawn to the 

 left; X and Y are for identification of the same points in plates 10 and 11, 

 Fisher, 1947; X 2. 



2, Frontal view of oral disk and tentacular fold of a small specimen from New- 



port Bay, Calif. The dotted circle indicates limit of oral disk, external to 

 which is the tentacular fold, subdivided into lobes; X 6. 



3, Tentacular fold of a large specimen from Anaheim Landing, Calif., having 



the dorsal lobes well developed (left side omitted) ; X 5. Vertical line of 

 dashes indicates sagittal plane. 



4, Longitudinal section of a portion of body wall to show integumental coelomic 



canals (IC) ; X 8. Circular muscle bundles in solid black. Longitudinal 

 muscle (LUT), seen from side, dotted. Arrows indicate passage to body 

 coelom. 



5, Cross section of body wall, cut slightly on bias; X 8. Four integumental 



canals are shown. The arrows are in the slits, shown in 4, between the 

 circular muscle bundles. On the right the cut is slightly to one side of 

 slits. Longitudinal muscles in solid black. 

 A, Accessory intestinal spiral; B, regular spiral; C, coecum, CV, dorsal contrac- 

 tile vessel (ventral in solid black); DT, dorsal tentacles; M, mouth; A^, 

 nephridium; RD, dorsal retractor muscle; RV, ventral retractor; S, spindle 

 muscle; W, wing muscles of rectum (the stippled bodies are the "Zottenbil- 

 dungen" of Selenka) ; A' and Y, second and first bends of accessory intestinal 

 spiral. 



Plate 19 



Xenosiphon branchiaturn (Fischer) 



1, Anterior sixth of a specimen, with introvert extended, from Panama. It 



has been opened a little to the left of middorsal line and spread out so that 

 the dorsal retractors are unnaturally spread apart and the rectum is on 

 extreme right instead of being in middorsal line. The esophagus actually 

 bends to left and is attached behind and in a line with the left dorsal re- 

 tractor; X 2. Figures denote muscle bands to right and left of nerve cord. 



2, Sketch of another specimen, from Panama, in which the introvert is partly 



withdrawn to show altered position of protractors (P); X 1. 



3, Brain and the bushy frons (cerebral organ) ; X 10. 



4, Six dermal rectangles at margin of papularium of La Paz specimen; X 10. 



In this specimen the cuticular welts above the canals alone show well, the 

 detail in upper left rectangle being supplied from a Panama specimen. 

 The next rectangle has no papillae but the irregular canal shows through 

 the cuticle. The lower left shows at each end of canal the pores (arrows) 

 which lead eventually to coelom. 



5, A single rectangle of skin of Panama specimen about 25 mm. anterior to 



papularium showing a skin canal gorged with material; X 20. At either 



end the dark spot marks the canal to coelom. 

 A, Anus; C, intestinal coecum; CV, dorsal contractile vessel; CF', ventral con- 

 tractile vessel; Fr, cerebral organ or frons; 7, introvert; A^, nephridium; NC, 

 nerve cord; 0, esophagus, its mesenteries cross-hatched; P, protractors of 

 head; R, rectum; RD, dorsal retractor; RV, ventral rectractor; S, spindle 

 muscle; T, tentacles, Z, filamentous organ described in text. 



441 



