54 ART. 4. — N. YATSU : 



approach the median plane until they fuse partially, assuming 

 the same shape as in the 7-8 p. c. stage. At the latter stage 

 the lobe (PI. VI., Fig. 84, and PI. VII , Figs. 91, 93, 94) is 

 situated at the centre of the shell and is the smallest of all the 

 lobes. It is nearly triangular in shape : posteriorly it reaches 

 the line connecting the otocysts : laterally it is limited by the 

 occlusores anteriores. In dorsal aspect the lobe is bifurcated in 

 the anterior half of its length, the gap between the two horns 

 being occupied by the dorsal mesentery. Eventually this lobe 

 becomes the so-called salivary gland of Cuvier ; it does not, of 

 course, differ structurally from any other liver-lobe. 



The posterior dorsal lobe is the lateral outgrowth of the 

 liver wall and hence it is the oldest of all the lobes. In 

 larvae of the 5-6 p. c. stage it is almost circular in outline 

 (PI. V., Figs. 77-80, and PI. VI., Figs. 81, 82, pst. dr. lv.). 

 By the 7 p. c. stage (PI. VI., Figs. 83, 84, and PI. VII., 

 Figs. 93, 94., pst. dr. lv.) it gives oft" anteriorly two cœca which 

 pass as far forward as the gastroparietal band {gst. bd.), just 

 beneath the otocysts (ot.). Posteriorly it extends as a pair of 

 posterior cœca as far as, or a little beyond, the posterior end 

 of the mid-gut (md. gt.). This part of the liver is the broadest 

 part of the alimentary canal, being so especially at the anterior 

 coecum, and gradually decreasing in breadth posteriorly. It 

 should here be noted that the size of the liver lobes varies 

 considerably according to the quantity of nutriment which it 

 contains. Whether the lame have recently fed can at once 

 be judged from the breadth of the liver, and indeed from that 

 of the posterior dorsal lobe alone, for this part of the liver is 

 bulged out laterally and can readily be seen. The median dorsal 

 portion of the liver shows but little swelling, though histologi- 



