THE LAMPREY. 13 



a ventral, which pass forwards, the one above, the other 

 below the line of branchial apertures, leaving these latter 

 uncovered. 



The dorsal muscle is inserted partly by a broad tendon to the posterior 

 dorsal cartilage ( 10), and partly into the fibrous posterior wall of the 

 orbit ; the ventral muscle is inserted by alongish tendon into the annular 

 cartilage ( 16). 



35. The great mass of radiating muscular fibre, which, 

 now the skin is removed, forms the outer surface of the oral 

 funnel. 



V. Make a median ventral incision through the skin 

 and muscle forming the walls of the body, begin- 

 ning about the middle of the body, and proceeding 

 forwards to within about half an inch of the last 

 gill-cleft, and backwards to within about an eighth 

 of an inch of the anus. From the ends of this 

 incision carry up vertical incisions on the left side 

 and remove the long flap thus made, so as to 

 expose the body- cavity from the left side. 

 Great care must be taken not to injure the liver 

 ( 37), the left kidney (40), or the rectum (39). 

 The following points can now be made out : 



36. The pigmented peritoneum lining the whole body- 

 cavity. 



37. The liver (Fig. 4, lr\ at the anterior end of the 

 cavity, deep red in the fresh condition in P. fluviatilis, 

 greenish in P. marinus. It consists of a single lobe, 

 convex on the ventral side, excavated dorsally for the 

 genital gland ( 38) and intestine ( 39), hollowed out 

 anteriorly for the pericardium ( 44), which it partly covers, 

 and ending in a blunt point posteriorly. 



38. The single genital gland (testis or ovary), oc- 

 cupying in the adult the greater part of the body cavity : 



