Gatty Marine Lahora'.ory, St. Andrews. 203 



Fiy. 5. The wall of the oesophagus, oes., as the sections proceed backward, 

 is completed, aud various blood-vessels, vv., including the 

 dorsal trunk, dv., are prominent. The lip-organ, Ip., presents 

 a basal mass with a central chink, and a regular arrangement 

 of its tissue. X oc. 2, obj. A. 



Fiy. 6. Vertical section of 0?t7en/rt/«ts//b>vn/s. «., the vestibule ; r., cen- 

 tral nervous system ; Ip., lip-organ ; mg., mucous gland ; sj^t., 

 septum. The section is imperfect at x. X about 40 diam. 



Plate VIII. 



Fig. 7. Transverse section behind the folds of the lip-organ and at the 

 point where the tendinous transverse band, bt., and its lateral 

 connections occur in the ventral region. X oc. 2, obj. A. 



Fig. 7 a. Transverse section indicating tlie condition of the parts of the 

 lozenge-shaped tendinous region ventrally, as its upper and 

 outer edges differentiate into muscular fibres and strands 

 pass into the fasciculi beneath. X oc. 2, obj. A. 



Fig. 8. Transverse section behind the foregoing, showing the diminishing, 

 pale, elastic band, bt., andthecompleteconditionof the ventral 

 longitudinal muscles, vm. The stomachal region is surrounded 

 by blood-vessels, bv. X oc. 2, obj. A. 



Fig. 9. Section in the line of the bristle-tufts with the opening of the 

 mucous gland, mp. The stomach is still surrounded by the 

 various vessels and their mesenteries. A trace of the elastic 

 system is seen in the muscular differentiation, wc, of the 

 mid-ventral area. X oc. 2, obj. A. 



Fig. 10. The thickening of the dorsal and ventral walls of the stomach 

 is conspicuous in this section (behind tig. 9). On the left is 

 a bristle-tuft, br. The median dorsal and ventral blood- 

 vessels and their mesenteries, and the ducts of the mucous 

 glands are seen on the way to the anterior. X oc. 2, obj. A. 



Fig. 18. Vertical section of the region of the collar, col., and the central 

 nervous system, c, with the adjoining body-wall. X oc. 4, 

 obj. D, with 2-iuch draw-tube. 



Plate IX. 



Fig. 11. The body-wall has attained its general arrangement with the 

 exception of the thickened lateral portions of hypoderm, hpe. 

 The coelomic space is large, and the median dorsal mesen- 

 tery is split inferiorly. The nerve-cords have now fused. 

 X oc. 2, obj. A. 



Fig. 12. In this section, which is posterior to the preceding, the vertical 

 elongation of the alimentary canal is noteworthy, and the 

 accompanying vessels are still separate, though in some fusion 

 is indicated. The coelom has its corpuscles, and the mucous 

 glands and their ducts are distinct. X oc. 2, obj. A. 



Fig, 13. Transverse section after a considerable interval backward from 

 the foregoing, showing the great extent of the ventral longi- 

 tudinal muscles, vm,, and the commencement of the male 

 gonads, g., below the gut. The large area occupied by the 

 intestine and its enveloping sinus is noteworthy, x oc. 2, 

 obj. A. 



