266 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



carrying the genital elements of individual A, and 

 the vaginal portion which receives the penis, and 

 with it the sperms, of individual B. There is not, 

 however, a complete partition between these three 

 portions. In section d the sperm groove and 

 oviducal portion are . separated completely from 

 the portion receiving the sperm of individual B. 

 The entrance of the spermatocyst into the fertilisa- 

 tion chamber is not shown. All sections drawn 

 under the Edinger Projection Apparatus, x 20. 



Plate VII. 



Fig. 21. Transverse section of a young individual, 9 mm. in 

 length when preserved. (The specimen was much 

 contracted.) The section passes through the 

 visceral hump, above which lie the mantle cavity, 

 the mantle, and the shell. Note that there are 

 differences between this and the adult stage, e.g., 

 the upward projections of the mantle have not 

 yet enclosed the shell, the opaline gland is pro- 

 portionately much larger and the purple gland 

 smaller than in the adult. The connective tissue 

 surrounding the organs is not shown. The section 

 was drawn under the Edinger Projection Apparatus 

 and is slightly diagrammatic. X 10-5. 



Fig. 22. Transverse section of the same individual as Fig. 21 

 passing through the buccal mass. The radula is 

 imperfectly developed. X 10-5. 



Fig. 23. Semidiagrammatic transverse section to show the 

 relations of the ganglia forming the circum- 

 oesophageal ring. The cerebro-pedal connectives 

 are not shown. The drawing has been made by 

 projecting structures occurring in five consecutive 

 sections each 10 jjl thick into one plane. The 

 telescoping chiefly affects the buccal ganglia, which 

 are situated slightly anterior to the other parts. 

 Drawn under the Edinger Projection Apparatus 

 from the same individual as the two preceding 

 figures. X 10-5. 



Fig. 24. Transverse section through the " tail " region of an 

 adult specimen to show the posterior pedal gland. 

 The gland consists of paired invaginations of the 

 foot opening by separate ducts to the exterior. 

 The section is somewhat oblique so that the duct 

 of the right portion of the gland is shown, but not 

 that of the left. X 34. 



