120 F. W. GAMBLE, M.SC, AND J. H. ASHWORTH, B.SC. 



Plate VI. 



FlG. 1. — The anterior end of a large specimen of the "Laminarian" variety 

 seen trom the left side, to show the external features, the segmentation of the 

 body-wall in relation to the internal metamerism, the nepl.ridal apertures, 

 and the commencement of the branchial region. The achpetous region fol- 

 lowing the fully everted buccal mass (Bucc. M.) extends forwards as far as 

 the groove indicating the inseition of the first diaphragm dorsally][ (Dphm. 1 ). 

 We have considered the first chpetigerous annulus and the annulus behind 

 this, as composing the first cheetigerous somite (/), although] we are fully 

 aware that, owing to the obliquity of the first diaphragm, and^the absence of 

 landmarks in the aclnetous region in front of this septum, it is somewhat 

 hazardous to delimit this first chpetigerous somite, x -f. 



FlG. 2. — View from the right side of two somites from the anterior part of 

 the branchial region of a specimen of the "Laminarian" variety 7 inches long. 

 The fourth gill is shown in detail, while the third and fifth are cut down to 

 the base of the main branches. The large size of the spreading branches and 

 the somewhat pinnate arrangement of the lateral twigs distinguish the gill of 

 this variety of A. marina from that of the ordinary shore lugworm seen in 

 Figs. 3 and 4. The webbing at the bases of the branches is generally much 

 more marked in old black examples than in immature dark red specimens 

 such as the present, x 14. 



FlG. 3. — Fifth gill of the right side of a shore lugworm 8 inches long, to 

 show the features characteristic of the littoral variety of Arenicola marina. 

 The branches are united by extensive connecting membranes, between which 

 the blood-vessels of the gill are faintly visible, x 14. 



Fig. 4. — The first gill of the right side from the same specimen as Fig. 3. 

 The ventral branches are apparently the last to develop, and are only just 

 budding oft" the secondary leaflets, x 14. 



Plate VII. 



FlG. 5. — Dissection of a large "Laminarian" variety, to show the general 

 characters of the internal anatomy (conf. pp. 9 to 10). The body-wall has 

 been cut along the mid-dorsal line, the flaps pinned back, and the alimentary 

 canal turned over to the left side. The special features shown are the 

 vascular system, the nephridia, the septa, and muscles, x 2. 



Plate VIII. 



FlG. 6. — View of a vertical longitudinal section of Arenicola marina taken 

 somewhat to the left of the middle line. The thickness of the body-wall is 

 exaggerated. The stomach has been cut away behind the heart, to show the 

 oblique muscles and the second nephridum. The main blood-vessels only are 

 indicated, the object of the figure being to show the exact position of the 

 three diaphragms (Dphm. 1_3 ), of the buccal or proboscidal sheath (B.Sh.), 

 and the relation of these to the external segmentation, x 3. 



Fig. 7.— Chitinoid spines covering the buccal papillae of that part of the 

 proboscis which is first protruded during eversion. They may be compared 

 with the figures of "hooks "from the proboscis of Sipunculids (e.g. Phascolion) 

 shown in Selenka, ' Die Sipunculiden.' Caustic potash preparation, x 50. 



