484 



ERNEST W. L. HOLT, 



ventral commissure entirely replaces the median vesicular band which 

 exists in front of it. 



The pituitary body 

 (woodcut -fig. 2 pt) is a 

 roundish mass of deeply 

 staining nucleated cells, 

 closely applied ventrally to 

 the membranous roof of 

 the mouth (m.) in the re- 

 gion of the pituitary space. 

 Anteriorly and late- 

 rally it is embraced by the 

 thick ventral wall of the 

 infundibulum {v. in.). 



This breaks down 

 above the pituitary body, 

 where by the latter be- 

 comes separated from the 

 infundibular cavity (m.), 

 only by a very delicate 

 membrane , containing 

 small scattered cells 

 {m.in). Immediately be- 

 hind the pituitary there lies the taperiûg downwardly bent anterior 

 extremity of the notochord. 



Fig. 2. Vertical transverse section , somewhat 

 diagrammatic, taken through region of pituitary space 

 of 1 day old herring. in. cavity of infundibulum, 

 m. in. membranous wall separating above from pituitary 

 body, TO. mouth cavity, op. hinder wall of eye, pt. pi- 

 tuitary body, tr. mesoblastic mass representing future 

 trabecular cartilage (cornu trabeculae) , v. in. ventral 

 wall of infundibular cavity. 



II. Early post-larval stage. 



Plate XXIX, figs. 8, 8 a, 8 b and 9. Plate XXX, fig. 10. 



A change is now noticed in the position of the cerebrum. As in 

 Elasmobranchs „an apparent rectification of the cranial axis" (Balfour, 1, 

 p. 398) has taken place, by the upward rotation of the cerebrum on 

 its posterior end. It now lies more or less parallel to the long axis 

 of the body. This change is doubtless due to the rapid development 

 of the trabecular and oral cartilages, and consequent forward dis- 

 placement of the mouth. The same cause seems to have determined 

 the withdrawal of the recess of the third ventricle from its position 

 beneath the optic commissure, for it is now seen in front of the same 

 (cf. figs. 4 and 9 r. v. 5., c. op.). 



The cerebrum tapers anteriorly and has a somewhat pyriform 



