MORPHOLOGY OF MELIBE 577 



designated the genital duct system in this niolhisc as con- 

 stituting a Fourth Type, During any ripe pliase of the 

 gonads the duct leading from the inactive area of an acinus 

 may be quite obscured by the ripening mass of germ-cells. 

 The organs of reproduction are represented in PI. 87, fig. 81. 



17. The spermatotheca I have called ovispermatotheca 

 because it is frequently filled with eggs from the oviduct. 

 The structure of the ovispermatotheca is quite peculiar owing 

 to the plicated nature of its lining. The cells lining this organ 

 are flask-shaped, the neck being longer than the body and 

 abutting into the cavity (PI. 37, fig. 82). 



18. The mucous gland is relatively rather large. A great 

 deal of mucus is formed by this gland at the time of oviposition 

 (Agersborg, 1919, 1921, 1923 a). Sections of the gland which 

 I have studied show that during the act of mucus-formation 

 the nucleus takes an active part. The nuclear membrane is 

 then very obscure or apparently absent, the nucleus goes 

 through fragmentation, the smallest cytoplasmic granules of 

 basophil nature are the nearest to the nucleus ; after the 

 mucous granules have liquefied and passed into the lumen or 

 cr.vity of the gland, the nucleus of the gland-cells is small, 

 shrunken, and non-granular, with a small nucleolus, and basal 

 in position within the cell. The cell then passes through a 

 period of refilling during which time the nucleus first grows in 

 size, and at the same time the micromeres of the cytoplasm, 

 which are lodged in the meshes of the reticular structure of the 

 cell, also grow. 



VI. Literature Cited. 

 Agersborg, H. P. Kjerschow (1916). — 'A study of the nudibranchiate 



mollusc, Melibe leonina (Gould).' A thesis submitted for the 



degree of J\Iaster of Science. University of Washington, Seattle. 



120 pp. of text and 53 plates. 

 (1919). — "Notes on Melibe leonina (C4ould)." 'Pub. Puget 



Sound Biol. Sta.', 2 : 269-77, 2 plates, 

 — — ^(1921). — "Contribution to the knowledge of the nudibranchiate 



mollusc, Melibe leonina (Gould)", ' Amer. Nat.', 55: 222-53, 



12 figures. 

 (1921a). — " On the status of Chioraera (Gould)"", 'Nautilus', 



35: 50-7. 



NO. 268 Q q 



