Galty Marine Lahoratory^ St. Andrews. 2G5 



Plate XI, 



lYff. IG. Vertical section of one half of the anterior end of Oirenia fusi- 

 formis cuttino- the nerve-centre, c, across, and showing its 

 relation to tlie sensory groove with its pigment-corpuscles 

 on the anterior wall, in close relation to the central nervous 

 system. A fold of the vestibule is seen at vt. x oc. 2, 

 obj. A, with 1-iucli draw-tube. 



Fig. 22. Transverse section a little beliind the tip of the snout of Myrio- 

 chele on the appearance of the pale central nervous system, r., 

 which becomes continuous witli the nerve-cord on each side. 

 The mottled condition of the hypoderm anteriorly is charac- 

 teristic of this form. X about 100 diam. 



Fig. 23. Horizontal section through the vestibule and three regions of 

 the alimentary canal, viz., ms., oesophagus, st., stomach, and 

 int., intestine, spt., septa ; val., valvular apparatus ; c, central 

 nervous system ; bv., blood-vessels, in some cases the dark 

 blood (coloured by haematoxylin) has been pushed beyond 

 the line of the vessel. X Zeiss oc. 4, obj. A, with l|-inch 

 draw-tube. 



Fig. 25. In this section the cords are descending, being a little below the 

 middle line, and the sides of the vestibule are now slightly 

 united. Dorsal and lateral blood-vessels are in a similar 

 position to those in the foregoing figure. X 100 diara. 



Fig. 26. The body-wall is completed, as also is the vestibule. The 

 nerve-cords, «c., are descending, and a section of the lip-organ, 

 Ip.f appears, x 100 diam. 



Plate XII. 



Fig. 17. Sagittal section of the anterior end, to illustrate the complex 

 interlacing of the muscular fibres. The collar, col., and 

 central neiwous system, c, are seen on the left. X oc. 2, 

 obj. A, with 1-inch draw-tube. 



Fig. 24. Transverse section before the completion of the body-wall. Tlie 

 nerve-centre, c, is well shown, and probably the lower ends 

 represent the commencement of the nerve-cords. Blood- 

 vessels, hv., occur both dorsally and laterally. X 100 diam. 



Fig. 27. In this section the outline of the body is slightly altered, the 

 vertical exceeding the transverse diameter, ocs., oesophagus 

 with its cellular lining ; Ip,, lip-organ and its radiate arrange- 

 ment of cells ; bv., blood-vessels. The dorsal and ventral 

 portions of the walls are much attenuated, partly from 

 stretching, x 100 diam. 



Fig. 28. The diminution of the dorsal hypoderm and the increase of the 

 ventral hypoderm are indicated in this figure, together with 

 the great size of the oesophagus. The nerve-cords are 

 approaching each other. X 100 diam. 



Fig. 29. Transverse section after the union of the nerve-cords, no. The 

 succeeding region of the canal is joining the oesophagus on 

 the right, and two mucous glands, mg., are cut obliquely. 

 X 100 diam. 



Ann. (fc Mag. N. Hist. Ser. 8. Vol xix. 18 



