48 W. A. HBRDMAN. 



longations of the liver can be followed with exactness until 

 their terminations in the body- wall are found. In one case, 

 for example, amongst our preparations the hepatic caecum 

 going towards the left rhinophore can be traced forwards 

 through sixty-six sections, gradually narrowing until it ends 

 blindly, the last section passing through its anterior wall. At 

 this point it has not nearly reached the base of the rhinophore. 



Dr. Bergh has figured^ the csecal extremities of the hepatic 

 diverticula in the terminal branches of the cerata as seen in 

 transparent preparations, and I freely admit that such appear- 

 ances are sometimes to be seen and that they look superficially 

 very like granular, dark-coloured liver cseca; moreover, when 

 one of the cerata is cut off near its base from a living Den- 

 dronotus the cut surface sometimes (i. e. in darkly coloured 

 individuals) shows an outer clearer zone, and then a dark 

 chocolate-coloured ring which is very suggestive of the hepatic 

 cseca, as seen in the cerata of some species of Eolis. Sections, 

 however, show that in both such cases, the terminal twigs and 

 the freshly cut stumps of the cerata, the appearance is due to 

 branching masses of pigment- cells lying in the solid mesoderm, 

 always a little way in from the surface and sometimes more 

 densely aggregated around the blood sinuses. I found that a 

 specimen killed and hardened rapidly, soaked in syrup and 

 gum, and cut at once in the freezing microtome without 

 staining, showed these pigment-cells much better than did the 

 specimens carefully hardened and stained and embedded in 

 paraffin. PI. VIII, fig. 19, shows the arrangement of the pig- 

 ment in such a fresh section: it is of a rich reddish-brown 

 colour. 



I believe, then, that the appearance of hepatic prolongations 

 in the cerata, which have been described by various careful 

 investigators, is due to the presence (1) of blood sinuses, and 

 (3) of a good deal of dark pigment in the mesoderm, and that 

 the hepatic caeca are not really prolonged into the cerata. 



Dr. Bergh has lately suggested to me in conversation that 

 possibly my results might be due to the caeca being contractile, 

 » Loc. cit., pi. ii, figs. 21, 22. 



