418 W. H. GASKELL. 



the cells of the arachnoidal tissue just as the increase of the 

 pigment in the branchial region, can be produced by a pro- 

 cess of malnutrition which causes at the same time extensive 

 passive degeneration of the red blood-corpuscles; and the 

 evidence here is just as striking as in the branchial region, 

 that this increase of the pigment is due directly to the 

 presence of pigment-bearing corpuscles. The natural conclu- 

 sion is that the pigment which is normally found in this situa- 

 tion is also due to the passive destruction of blood-corpuscles, 

 and that therefore these lines of pigment represent closed-up 

 vascular spaces in between the cells. 



If, then, these cells represent the cells of the old cephalic 

 liver of the Crustacean-like ancestor, a straightforward explana- 

 tion of the pigment between them, and of the formation 

 of the dorsal and ventral sinuses, is afforded by the supposi- 

 tion that the whole represents the blood spaces and blood 

 channels by which the liver-cells were originally supplied with 

 blood. 



The interpretation of the pigment found in other places, 

 such as that in connection with the branchiee, upon the 

 hypothesis that such pigment denotes the locality of previously 

 existing lacunar blood spaces, will be dealt with in the next 

 chapter, where I shall consider the formation of the present 

 alimentary canal. 



Sect. 7. — The Relation of the Supra-oesophageal 

 Ganglia to the Walls of the Cephalic Stomach. 

 Upon the supposition that the Ammocoetes is derived 

 directly from a Crustacean-like ancestor, we ought to find that 

 the supra-cesophageal ganglia are situated in front of the 

 oesophagus, close against the anterior rounded termination of 

 the cephalic stomach on each side of the middle line; and 

 these supra-oesophageal ganglia ought to form — (1) olfactory 

 lobes giving origin to olfactory nerves, (2) cerebral hemispheres 

 giving origin to no outgoing nerves, and (3) an optic portion 

 which gives origin to the optic ganglia and nerves of eyes of 

 an Arthropodan type. Further, seeing that the nervous 



