238 FISH. [Vol. X. 



according to Sagemehl (46). He proposes to call the pia or 

 its homologue the primary vascular membrane. Fulliquet (12) 

 accepts this view for the conditions found in the Protopterus. 

 Burckhardt (3), in his studies of the Protopterus, describes the 

 pia and arachnoid, but has nothing to say of the dura. He 

 discovers a structure along each side of the myel homologous 

 to the ligamentum dentatjim of higher forms. He has also 

 found it in the sturgeon, but divided, one part being nearer 

 the dorsal root, the other nearer the ventral. He considers it 

 a differentiation of the pia, and supportive or protective in 

 function on account of the great lateral mobility of these forms. 

 Mrs. Gage (13) finds all three of these membranes represented 

 in the Diemyctylus. The dura is characterized by numerous 

 large pigment cells. It lines the cranial cavity, sending off an 

 almost complete investment for the supraplexus, and a partial 

 one for the hypophysis. It follows out the cranial nerves, and 

 surrounds their ganglia. She finds that the pia does not 

 always follow the outline of the brain closely, but sometimes 

 lies nearer the dura, probably an effect of hardening. It forms 

 a single layer between the hemicerebrums, and contains blood- 

 vessels ; it separates the hypophysis from the infundibulum, 

 and forms a continuous sheet over the epiphysis. The arach- 

 noid is represented as a spongework, formed of connective 

 tissue cells. 



In the Desmognathus the conditions are substantially the 

 same as in Diemyctylus. The dura seems to lose its pigment 

 cells along the floor of the cranium. The pia is quite closely 

 adherent to the nervous substance. It consists of a thin layer 

 of cells the even contour of which is occasionally broken by 

 the slight elevation of their nuclei. In or upon this layer are 

 the blood-vessels. A complete investment or separation of the 

 hypophysis from the infundibulum could not be satisfactorily 

 demonstrated. Numerous pigment cells are found in the meta- 

 plexus, as well as in the dura. 



The arachnoid is represented between the two membranes 

 just described by loose trabeculae of connective tissue. It 

 entirely disappears along the base or ventral aspect of the brain 

 and myel, on account of the meeting of the pia and dura along 



