The Brain of Diemydylus Viridescens 313 



the right interrupted lines represent the cerebrum raised to an upright 

 position and the pallium folded to form a paraplexus v. 



Fig. 98. Shows the infundibulum with the hypophysis surrounding 

 the cephalic extension ; the pallium passing at the right from the sul- 

 cus si laterad and giving off the paraphysis, or dorsal sac, in which is 

 embedded the epiphysis at the left of the meson. 



Fig. 99. Shows the caudal projection from the paraphysis over the 

 supracommissure and habense, and hence the manner in which cinerea 

 surrounds the habena ; and the sulcus ventrad of the habena which is 

 continnous with si of Fig. 98. 



Fig. 100. Shows the union of the geminums and the relation of the 

 caudal extensions from the infundibulum. 



Fig. ioi. A transection of the brain of a large red diemyctylus, be- 

 ginning to transform. X 22. Through the precommisure, near the 

 level of Fig. 17 but shows the hemicerebrums much divaricated as is usual 

 with the red forms. At the right, interrupted lines indicate the position 

 of the cerebral walls, as though raised and carrying the plexus with 

 them (cf. Fig. 97). 



Fig. 102. The outline of a transection of the brain of a young lepi- 

 dosteus, at a level corresponding with Fig. 97, copied from Wilder (50). 

 This shows that in a young ganoid the cerebral walls occupy practically 

 the same position as indicated by the interrupted lines of Fig. 97. 



Fig. 103. A view of the cephalic half of the brain of a larval lamprey, 

 12 cm. long, from the morphological meson. X about 40. From the 

 great development of the right habena (Fig. 107) the niesal parts are 

 pushed to the left. The epiphysis and its stalk are shown as mesal 

 structures. The pigment shown here as black is really a brilliant white 

 by reflected light. The supra- and postcommissures are elongated 

 structures, the mesoplexus sends a diverticulum cephalad over the lat- 

 ter (Fig. 109). The rhinocoele extends cephalad, the paraccele caudad 

 from the common opening shown as deeply shaded. The precommis- 

 sure is dorsad of the porta (Fig. 104). Another band of alba at an. 

 corresponds in position (Fig. 105), with reference to the chiasma, to 

 cm. of Fig. 93. The infundibulum has a cephalic and caudal prolonga- 

 tion, with the former is associated the hypophysis. The optic nerve 

 extends caudad to the eye. 



Fig. 104-111. Transections of the same. X 40. 



Fig. 104. Through the epiphysis, its stalk, the paraphysis (p. 285) 

 and the tip of the left habena which protrudes into it. 



Fig. 105. Through the portae, the pallium and the opening of the 

 paraphysis. st indicates a possible striatum. 



Fig. 106. Through the cerebrum and the habense, to show the relation 

 of the pallium to the latter. 



Fig. 107. Through the habenae and supracommissure near the point 

 where the stalk of the epiphysis opens into the diacoele. 



Fig. 108. Shows the membranous roof of the mesencephal, the meso- 

 plexus with a mesal fold and the sulcus .y in the walls of the geminum. 

 The large cell at d forms a ridge. In this and similar ridges the large 

 cells are arranged. 



Fig. 109-110. Portions of enlarged sections through opening of the 

 epiphysis and the postcommissure and cells of the torus. 



Fig. III. The dorsal part of a section just cephalad of the closure of 

 the myel to show a minute sac of endyma, in the position of a metapore. 



