318 ELEMENTARY BIOLOGY. [CHAP. 



d. Insert the point of a scissors into the pallial lobe 

 immediately above the gill laminae, and make an 

 incision which shall pass under the posterior 

 adductor muscle and immediately over the line of 

 attachment of the outer gill-lamina. A large 

 opening will be found in the dorsal middle line, in 

 the region of the posterior adductor muscle; insert 

 the scissors blade into this and cut obliquely 

 backwards. There will now be laid bare the 

 supra-branchial or doacal chamber. 



a. Follow its boundaries. It ends blindly in front, 

 immediately above the most anterior point ot 

 attachment of the gills. It opens posteriorly by 

 two orifices; a dorsal median one referred to 

 above, and a posterior one, whose lips are 

 produced into a short smooth-walled dorsal 

 siphon. It is walled in dorsally and externally 

 by the pallial lobes and ventrally by the gill- 

 laminae. 



ft. The suspensory ligament of the gills can now be 

 seen ; it is a membranous fold arising immediate- 

 ly beneath the posterior adductor muscle. In- 

 sert a seeker from below into the supra-branchial 

 chamber, through the cleft between the body 

 wall and inner gill-lamina. It passes internally 

 to this ligament, which therefore subdivides the 

 greater part of the supra-branchial chamber into 

 two portions, each of which is in open commu- 

 nication with one gill-cavity. 



y. Remove the anterior portion of ft and note, 

 opening into the inner subdivision of the supra- 

 branchial chamber, the genital and excretory 



