Kingsbury, Encephalic Evaginatiojis in Ganoids. 41 



lum caudad of the velum exists, but the closer approximation 

 of cerebrum and geminum renders it far less conspicuous. The 

 slightly recurved lobes also do not form the interval occupied in 

 Aniia by the cephalic portion of the diverticulum, and this in 

 Lepidosteus is flatter. The caudal portion is also extensive and 

 reaches at least to the cerebellum, but here a complication ex- 

 isted which prevented the caudal limit being ascertained; name- 

 ly, the presence of similar lateral extensions of the membran- 

 ous roof of the metencephal. Some distance caudad of the 

 metatela lateral pockets appear upon the sides of the oblongata 

 (or myel) which farther cephalad are seen to be from the meta- 

 plexus. From the point where they join the metaplexus ceph- 

 alad there is a lateral extension of the cavity, or rather more 

 correctly, a series of lateral extensions which in some regions 

 reach to the ventral surface of the brain and almost meet each 

 other at the ventrimeson ( Fig. 5). There is also a projection 

 of the metatela over the surface of the cerebellum. 



The membranous roof of the prosencephal, the mesal 

 fold from it, the dorsal sack and velum and the metaplexus in 

 Amia and Lepidosteus are lined with an endymal epithelium of 

 large columnar cells which are of the appearance characteristic 

 of secreting cells.; the nucleus is situated in the base and the 

 cell body stains but lightly, resembling some mucous cells. 

 The lateral diverticula are also lined by such cells, but only on 

 their ectal side ; the ental side toward the brain, being very del- 

 icate and lined with flattened cells. The membranous roof of 

 the fore-brain, the velum and mesal fold are all richly supplied 

 with blood vessels, or blood spaces, and the ectal surface of the 

 diverticula is also similarly supplied. We cannot doubt that 

 the columnar cells of the membranous portions of the brain 

 roof are of use in the elaboration of the coeliolymph. Vascu- 

 lar portions of the telas of the brain, generally appearing as 

 plexuses, are of quite usual occurrence, and must have an im- 

 portant function in the nourishment of the organ. The only 

 explanation of these diverticula that appeals to me is that they 

 are for the increase of secreting surface. This may be accomp- 

 lished in either of two ways, by reduplication, as in the forma- 



