122 F. W. GAMBLE, M.SC, ^ND J. H. ASHWORTH, B.SC. 



FlG. 22. — Transverse section of the body a short distance behind the third 

 diaphragm at the level of the openings of the oesophageal pouches ( GL. Op. ), 

 The external aperture of the second nephridium is shown on the right side. 

 The subdivision of the body-cavity into three longitudinal portions, and the 

 structure of the oesophageal pouches, are well seen, x 38. 



Fig. 23. — Transverse section of the body in the branchial region at the 

 level of a parapodium. The neuropodium is cut through its entire length on 

 the left side. On one side of the nerve-cord a retractor muscle from the 

 notopodium arises, on the other an oblique muscle. The vascular supply of 

 the body-wall, setse, and gills is well seen, x 38. 



Plate X. 



Fig. 24. — Amoeboid and spindle-shaped cells of the coelom. x 1000. 



Fig. 25. — Sagittal section of the brain slightly to the left of the middle 

 line, from a young littoral form about 3 inches long. The mass of ganglion- 

 and glia-cells underlying the epithelium of the prostomium is distinct ; some 

 of the cells of the latter are shown bearing sensory processes. The nuchal 

 organ, Nu, is cut at its full depth, x 85. 



Fig. 26. — View of a dissection of the brain, oesophageal connectives, oto- 

 cysts, and the buccal sheath. The commencement of the neural vessels from 

 capillaries of the organs just mentioned, is shown. Seen from the dorsal 

 surface. The buccal mass, cut transversely, lies in the centre of the figure, 

 x 6. 



Fig. 27. — An otocyst with the otoliths composed of quartz grains. The 

 sensory epithelium and the surrounding nerves and supporting cells are seen. 

 x 160. 



Fig. 28. — Otoliths to show the chitinoid covering of the quartz grains, 

 x 500. 



Fig. 29. — Ripe spermatozoon seen on March 10th, 1S97. Length of head 

 4 //., length of tail 54 /*. x 3000. 



Fig. 29a. —Head and portion of tail of an immature spermatozoon seen on 

 February 22nd, 1897. x 3000. 



Figs. 30 — 34. — Stages in the development of the spermatozoa. 

 Fig. 30. — The 8-celled stage, in which the spermatoblasts leave the 



testis, x 500. 

 Figs. 31 and 32.— Later stages, x 500. 

 Fig. 33. —Two cells from a stage much later than the preceding, showing 



the commencement of the tail, x 2000. 

 Fig. 34. — Discoidal mass of almost ripe spermatozoa, x 500. 



Fig. 35. —Developing ova. {a and b) show a polar body (?) x250. (c) is a 

 ripe ovum enlarged 125 times. 



Fig. 36. — Longitudinal section of the heart of an Arenicola 250 mm. in 

 length, to show the cardiac body, x 32. 



Fig. 37. — Histology of a portion of the cardiac body of fig. 36. x 500. 



Fig. 38. — Longitudinal section of the heart of a young Arenicola 65 mm. 

 in length, to show the cardiac body at an early stage of development, x 50. 



