1922. No. 5. ARIONIDAE OF NORWAY. 



branch to the lover tentacle. The pharyngeal retractor originates a little 

 behind the former ones, and, passing forward, bifurcates into two branches 

 which pass through the nerve ring and attach themselves to the buccal mass. 



In adults the reproductive organs chiefly fill up the primary body- 

 cavitv in the region under and a little behind the shield ; the dark, oval, 

 hermaphroditic gonad or ovo-tcstis {g.), however, is lodged in the liver 

 far behind. Eggs and sperms pass the narrow, sinuated hermaphroditic 

 duct [ductus hermaphroditicus, d. Ii.) to the broader, tortuous o vis perm a- 

 toduct (o.-sp.-d.). The latter contains only. one cavity, consisting of two 

 joined grooves, one of which is for the sperms, the other, with swollen 

 walls due to the numerous glands of the wall, for the eggs. Where the 

 hermaphroditic duct joins the ovispermatoduct there is situated the large 

 albumen gland [a. gl.). 



After the ovispermatoduct the male and female parts of the repro- 

 ductive organs separate, to join each other before the aperture. The former 

 consists of the vas deferens [v. d.) and further on of the epiphallus \rp.), 

 the latter of the oviduct (0.), often also called the free oviduct 

 to distinguish it from the female part of the ovispermatoduct. Like the epi- 

 phallus and the oviduct the sperm a thee a or rcccptaciduni seim'/iis irec.) 

 opens into the atriiuii iafr.) or vestibule, the wall of which in its lower 

 parts contains numerous glands. A genital retractor {retr.) attaches itself 

 by one branch to the oviduct, and by the other to the stalk of the sperma- 

 theca. — In the epiphallus there is formed the sperm atop h ore, contain- 

 ing the sperms. 



Under the shield we find three chief palliai (or mantle) organs: 

 the heart, surrounded by the kidney, and the lung. Enclosed in the 

 pericardium or seconder y body- cavity (a part of the reduced coelom), 

 the heart consists of two chambers, an auricle, which receives the blood 

 from the lung, and a muscular ventricle. The latter gives oft" a short artery 

 which branches oft' into the aorta anterior \a. a.) lor a. cep/ia/ica) and the 

 aorta posterior (a. p.) (or a. intesti/ia/is). (In the figure both are cut across 

 and the points of separation are conformably designated through xx and 00). 



The cavity of the respiratory organs surrounds the heart and 

 kidney in the shape of a ring, opening outwards through the respiratory 

 aperture or pneumostome (/>;/. I. A plexus of blood vessels projects into the 

 cavity, from the roof (r. /.I as well as from the floor or diaphragma {/. /.); 

 in the figure the latter has been cut free and folded over so as partially 

 to cover the heart, in order to aftbrd a view into the lung. 



The kidney or uep/iridiuiii [k.) surrounds the heart in the shape of 

 a ring, forming the central wall of the lung cavit}-. Erom the kidney the 

 excretory substances pass through the ureter, which, adherent to the left 

 side of the kidney, first extends backwards and then in the opposite direc- 

 tion, to open into the respirator}' orifice close to the rectum. 



