53 



each is lined partly by ciliated and partly by 

 germinal epithelium. X 200 diam. 



Fig. 5. Transverse section of mantle of spawning male 

 Mussel (New Brighton beds, July). A sperm 

 tubule is shown, partly lined with ciliated 

 epithelium. Note the great development of the 

 reticular tissue. X 230 diam. 



Fig. 6. Transverse section of mantle of completely spent 

 female Mussel (Barrow Channel, August). X 35 

 diam. 



Fig. 7. Portion of transverse section of mantle of female 

 Mussel (Barrow Channel, September 30). A 

 developmg ovarian tubule is shown. Actual 

 size = 0*568 mm. Note the proliferating germinal 

 epithelium, and the ciliated strip of wall. X 660 

 diam. 



Kefeeence Letters. 



abd., abdomen; add. a., anterior adductor muscle of 

 the shell; add. p., posterior adductor muscle of the shell; 

 br. B., right gill ; br L., left gill ; bl. sp., blood space ; cr. 

 St., crystalline style; ep. ger., germinal epithelium; ep. 

 cil., ciliated epithelium; ep. ext., external epidermis 

 of mantle; int., intestine; Mn. L., left mantle lobe; Mn. 

 jB., right mantle lobe ; j9e;*., pericardial cavity; per. gid., 

 pericardial gland and auricle ; pp. gen., right genital 

 papilla ; pa. d., right dorsal labial palp ; pa. v., right ventral 

 labial palp; re)i., renal organ; ret., reticulum of mantle; 

 ret. bi/s., retractor muscles of the byssus ; ret. bys. in., 

 insertion of retractor of the byssus into the shell; rect., 

 rectum; sup. fil., supporting filaments in sperm tubule; 

 St., tubular portion of the stomach ; sp., rows of mature 

 spermatozoa; tub. ov., ovarian tubule; vise. «i;., visceral 

 nerve cord. 



