362 



MOLLUSC A. 



two papillne leads into a large sac — the nephridial sac. But the two 

 sacs are united by two bridges, and they give off an unpaired dorsal 

 elongation, which extends as far back as the reproductive organs. 



The dorsal wall of each nephridial sac becomes intimately associated 

 with the branchial veins, and follows their outlines faithfully. It is - 

 likely that waste material passes from the blood through the spongy 

 appendages into the nephridial sacs. 



Into the terminal portion of each nephridial sac, a little below its 

 aperture at the urinary papilla, there opens by a ciliated funnel another 



sac, which is virtually 

 jc the body cavity. It 



^J'i surrounds the heart and 



other oigans, and is 

 often called the viscero- 

 pericardial cavity. 

 Through the kidneys 

 or nephridial sacs it is 

 in communication with 

 the exterior. 



Reproductive 

 system. — The 

 sexes are separate, 

 but there is not 

 much external differ- 

 ence between them, 

 though the males are 

 usually smaller, less 

 rounded dorsally, 

 and have slightly 

 longer arms. When 

 mature, the male is 

 easily known by a 

 strange modifica- 

 tion on his fifth left 

 arm. The essential 



reproductive organs are unpaired, and lie in the body cavity 



towards the apex of the visceral mass. 



The testis — an oval yellowish organ — lies freely in a peritoneal sac, 

 near the apex of the visceral mass. From this sac the spermatozoa pass 

 along a closely-twisted duct — the vas deferens. This expands into a 

 twofold " seminal vesicle," and gives off two blind outgrowths, of which 

 one is called the " prostate." The physiological interest of these parts 

 is that within them the spermatozoa begin to be arranged in packets. 

 In this form they are found within the next region, the spermatophore 

 sac, which opens to the exterior to the left of the anus. Each spermato- 



Fig. 157. — Diagram of circulatory and excre- 

 tory systems in a Decapod-like Sepia. — After 

 Pelseneer. 



j , Gill ; 2, renal sac ; 3, afferent branchial vessel ; 

 4, branchial heart ; 5, abdominal vein ; 6, heart ; 

 7, viscero-pericardial sac (body cavity) ; 8, genital 

 organ; 9, posterior aorta; 10. "auricle' ; 11, 

 glandular appendage of branchial heart; 12, renal 

 appendages of branchial vein ; 13, external aper- 

 ture of kidney ; 14, vena cava ; 15, anterior aorta ; 

 16, bifurcation of vena cava; 17, reno-pericardial 

 aperture. 



