42 r. W. GAMBLE AND J. H. ASHWORTH. 



and f^lia-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 tiie 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 nervous 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 lOlh, 1897. Length of head 

 4 /t, length of tail 54 fi. X 3000. 



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

 on February 22nd, 1897. X 3000. 



Fifis. 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 (?) x 250. 

 (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. 

 Pig. 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. 



