94 LOLIGO PEALII. 



m) Note, in the posterior region of the rectum, a pair of small protuber- 

 ances or papillae. On these are located the external openings of 

 the kidneys. The latter are merely capsules or cavities with such 

 delicate walls that their form and extent can be demonstrated only 

 by reference to certain parts of the blood circulatory system. 



Exercise 3. Begin a sketch of the mantle cavity on a convenient scale, 

 labeling all of the organs thus far determined. 



THE CIRCULATORY SYSTEM. Locate and study the following parts 

 of the circulatory system and get a clear idea of the course of the blood : 



a) At the base of each gill is a rounded, light colored organ, the 



branchial heart. A branchial artery, running thence along the 

 dorsal side of the gill, carries the blood to the latter organ to be 

 oxygenated. 



b) Three sets of vessels bring the blood to the branchial hearts. 



These are the anterior venae cavae, the posterior venae cavae, 

 and the mantle veins. The single trunk of the anterior vena 

 cava may be seen emerging from beneath the posterior opening of 

 the siphon and passing back under the rectum. Just anterior to 

 the external openings of the kidneys it divides, one branch passing 

 around each side of the rectum and entering the cavity of the cor- 

 responding kidney. Here the branches widen into the glandular 

 portions of the anterior venae cavae, which, being easily made out, 

 help to determine for the student the position and extent of the 

 kidneys. 



c) The posterior venae cavae may be seen to spring from the mantle 



laterally to the anterior end of the visceral sac. Each widens 

 rapidly and runs forward to the region of the branchial hearts. 

 Between the latter each terminates in a small glandular portion 

 connected with the corresponding division of the anterior vena and 

 occupying the posterior part of the kidney capsule. The connec- 

 tions of these glandular portions with each other and with the 

 branchial hearts can not be demonstrated in this dissection. 



d) Lift up the gills and note on each side, the mantle vein arising from 



