VERTEBRATES FROM A ORUSTAOEAN-LIKB ANCESTOR. 405 



anterior end of the cephalic stomach_, and is directed tailwards, 

 terminating at the commencement of the notochord ; this 

 forms the remnant of the original oesophagus. The other 

 tube, compressed to form a vertical slit, leads out of the fourth 

 ventricle, i. e. out of the pyloric end of the cephalic stomach, 

 and is directed headwards, terminating also near the commence- 

 ment of the notochord. This latter tube is in my opinion the 

 remnant of a single median duct of the cephalic liver, which in 

 the Crustacean ancestor opened into the pyloric end of the 

 stomach on the ventral side. In the diagram already referred 

 to (PI. XXVIII, fig. 29) I have indicated how the liver-duct 

 and oesophagus from the Crustacean cephalic stomach would 

 form the projections known as the conus post-commissuralis 

 and the infundibular projections. If this interpretation is 

 true, we ought to find evidence of the vestiges of the large 

 cephalic liver in connection with the termination of this duct. 



In the description of the external surface of the brain I 

 have already described how the brain is covered over with a 

 glandular-looking organ containing a large amount of pigment 

 arranged in irregular clumps and lines, and I have described 

 also the general arrangement of this tissue on the brain surface. 

 It forms what is called by Ahlborn the " arachnoidale Fiill- 

 gewebe,"' and is looked upon by him and other observers, 

 e. g. Sagemehl (15), as a peculiar kind of connective tissue 

 somewhat allied to fat tissue. 



Peculiar the tissue undoubtedly is, but that it bears the 

 slightest resemblance to any form of connective tissue, whether 

 fat-bearing or otherwise, I entirely deny. It presents the 

 exact appearance of a compact mass of large gland-cells belong- 

 ing to some such organ as a liver, each cell containing a 

 central nucleus surrounded by the remains of the protoplasmic 

 cell-contents. These cells are pressed closely to each other in 

 all directions, so as to form a bilaterally symmetrical organ as 

 described on p. 384, the glandular nature of which is in my 

 opinion fairly evident. The arrangement of the cells is seen 

 in fig. 16, PI. XXVI, which represents a magnified portion 

 of an osmic preparation from the series represented in figs. 



