200 ARTHUR 11. SHIPLET. 



this vessel, filling up the space between the two sides of the 

 spiral valve, is a quantity of fatty tissue. The cilia on the 

 inner face of the spiral valve are very evident. 



The lumen of the mid-gut is so large that almost the whole 

 of the body cavity in that region of the Ammocoete is taken 

 up by this part of the intestine; consequently the liver, the 

 only gland opening into the mid-gut, is pushed forward and 

 lies on each side and below the oesophagus. This gland has its 

 origin at a very early stage, about the fourteenth day, as an 

 evagination of the mid-gut, whilst the latter is still crowded 

 with yolk. The diverticulum thus produced grows out in the 

 ventral side of the alimentary canal into that space between 

 the hypoblast and epiblast which was mentioned above as 

 being crowded with blood-corpuscles. This space subsequently 

 becomes enclosed by definite walls by the downgrowth of the 

 mesoblast in this region. It becomes the subintestinal vein 

 which still continues to supply the liver with venous blood. 

 The single diverticulum soon begins to branch, and at an early 

 stage one of the branches becomes diff'erentiated from the 

 others, acquires a large lumen, and forms the gall-bladder. 

 The cells forming the liver are cubical with large nuclei, they 

 do not appear to have a definite outer layer of flattened cells, 

 though occasionally such a cell is present. In the older larvae 

 the gall-bladder has a great relative size. It lies embedded in 

 the liver on the right side of the oesophagus. The bile-duct 

 runs from it above the mid-gut, bending down to enter the 

 mid-gut in the spiral valve on the left side. 



The hind-gut is smaller than the mid-gut, its anterior limit 

 is marked by the termination of the spinal valve, which does 

 not extend into this region. The two segmental ducts open 

 into it just where it turns ventrally to open to the exterior by 

 a median ventral anus. Its walls are in this region slightly 

 puckered. The cells lining it are not so high as in the other 

 parts of the intestine, but more cubical. 



Its lumen is from an early stage lined with cells which 

 have lost their yolk, and it is in wide communication with the 

 exterior from the first. This condition seems to be, as Scott 



