332 



MR. A. E. SHIPLEY ON THE GENITS SIPTnyCtTLtTS. [Apr. 18, 



(2 )Selbnka, E. — Die Sipunculiden. Eine systematische Mono- 

 graphie. Eeisen im Archipel der Philippinen, Bd. iv. 

 Abth. 1. 



(3) Waed, H. B. — " On some Points in the Anatomy and 

 Histology of Siptinculus ntirhis, L." Bulletin of the Museum 

 of Comparative Zoology at Harvard College, vol. xxi. 

 No. 3. 



(4) DA]!fiELSSES- and KoEEif . — Grephyrea. Den Norske Nordhaus- 



Expeditiou. Part iii. 



EXPLANATION OF THE PLATES. 

 List of Reference Letters. 



Fig. 1. View of a Sipunculus indicus cut open by an incision a little to the 

 right of the dorsal middle line. The introvert is extended and the 

 viscera are exposed in situ. The drawing is | the natural size. 



2. A portion of the same in the region of the oesophagus, magnified two 



diameters, to show the numerous bands of longitudinal muscles. 



3. Two views, magnified, of the brain of Sipunculus tensdlatus. The fig. 



to the right shows its position above the oesophagus and between 

 the dorsal retractors. The fig. to the left is more highly magnified, 

 to show the character of the digitate processes. 



Plate XXVI. 



Fig. 4. A view of the head of <S. indicus. The mouth is shown in the centre, 

 and between it and the riug of tentacles run several vascular ridges. 

 To the right are two sketches, more highly magnified, to show the 

 characters of the scales on the introvert and the square areas in 

 the trunk. 



5. A dorsal view of the head of 8. nudus with the tentacular fringe very 



much folded, X 4. The mouth is away from the spectator and the 

 depression leading to the brain is near him. 



6. A ventral view of another specimen of <S'. nudus, in which the fringe is 



not at all folded, the wall of the oesophagus is bulged forward and 

 obliterated the oral orifice. 



7. An anterior view of the mouth of S. tessellatus. 



8. A longitudinal section through the skin of the introvert of S. indicus, 



showing the structure of the scales, the prolongations of the body- 

 cavity into them, and the ' papillse.' 

 A view of the rectum of S. tessellatus, showing the anal tufts, the 

 enlargement of the alinLentary canal to form the rectum, the spindle 

 muscle, the muscular stfands siij'iporting the intestine, the ciecum 

 opening into the latjt'er, aji&,t-he longitudinal and circular muscles of 

 the skin. " . • ■■ '■ ■ ■ . 



9. 



