INVERTEBRATE ZOOLOGY. 129 



themselves. The water enters the infra-branchial chamber through the 

 branchial siphon, passes through the water-pores into the supra-branchial 

 chamber and out throiigh the cloacal siphon. The incurrent water brings 

 with it nutritive material which is taken up hy the mouth, and the water in 

 the supra-branchial chaml)er receives waste material from nephridia and rec- 

 tum, as well as the generative products. 



2. Circulatory system. Heart with median ventricle, perforated by intes- 

 tine, and two lateral auricles which lie at the base of the gills and receive 

 from them the aerated blood. From the ventricle proceed anterior and j^oste- 

 rior aortae, which l)ranch into arteries that stipph' the body. From the open 

 termini of these, the blood passes into a lacunar system, through which it is 

 conveyed to the gills. 



3. Excretory system. The paired organ of Bojanus lies below and some- 

 what posterior to the heart. Remove the gills at their base, and open the 

 supra-branchial chamber laterally. The organs appear as greyish-yellow 

 masses, and show a minute opening near their anterior end, the opening of the 

 ureter. The nephridial openings lie in the floor of the pericardial chamber 

 (^coelom), and may be demonstrated by opening the chamber dorsally and 

 removing the heart. 



4. Digestive system. To dissect this, commence at the rectum and trace 

 the canal in an anterior direction to the mcmth. It consists of a long, coiled 

 tube, running through the pendulous bodj', and closely packed in on all sides 

 by the liver above and the reproductive gland below. The muscular wall 

 of the body should be removed and the canal carefully separated from the 

 surrounding mass. A transparent rod is generally present, lying in the intes- 

 tine in tlie hepatic region. Its iise is unknown. 



5. Reproductive system. Bisexual, the male and female glands closely re- 

 sembling each other. The germ-glands are very numerous whitish masses, in 

 structure like bunches of grapes. The terminal duct collects the germ-cells 

 from all the bunches, and opens into the supra-bi-anchial chamber, at the end 

 of a \itt\Q x>apilla , which projects from the wall of the body just anterior to 

 the opening of the ureter, 



6. Kebers Organ. A brownish mass Ijing upon the mantle just under the 

 hinge, and between the liver masses and the organ of Bojanus. Its use is 

 unknown, but it is probably connected with. circiTlation or excretion. 



7. Neii'ous sy.'item consists of three main double ganglia connected with 

 commissures, and of nerves which proceed from the ganglia and supjily the 



