17 



epithelium. These cells, however, do not enclose any 

 canal. It appears as if the secretion must reach the 

 groove by passing through the cells. Usually in sections 

 there are no traces of secretion in the groove, and in living 

 specimens no mucus or other fluid appears coming from 

 the groove. What is, then, the function of the gland? It 

 is homologous with the pedal pore of many other gastro- 

 poda ; once considered an aquiferous pore by which water 

 entered the animal. The gland secretes the substance of 

 which the egg capsules are formed. This fact, noted in 

 1899 by Cunningham to apply to Buccinum and Murex, 

 has since been found to be true for Purpura by Pelseneer. 



The Mantle and Pallial Cavity. 



The pallial cavity proper is the space between the 

 mantle and the dorsal surface of the body of the animal. 

 Its floor is formed by the body wall, its roof by the mantle. 

 It will be advisable to refer in a general way to this part 

 of the animal in a separate short section, inasmuch as the 

 cavity contains several important organs belonging to 

 different systems. 



These organs considered together may be termed the 

 Organs of the Pallial Complex. Three of them are 

 structures developed largely from the mantle itself — the 

 ctenidium or gill, the osphradium, and the mucous gland 

 (PI. II, fig. 8). Furthermore, there are to be considered 

 the Eectum and Anal opening (fig. 8, Red.), the Eenal 

 opening, and the male and female genital openings. The 

 mantle itself is thick and muscular, and this applies most 

 markedly to the free edge. The edge is slightly recurved 

 outwards, and just behind the extreme margin and on the 

 outer surface is a delicate band of yellow pigment. 



If the mantle is slit down the extreme right side on 

 the left of the rectum (and the oviduct in the female), 



