Observations upon tlio Development of tlio Toleostcan Hrain. 479 



though frequently satisfactory, is not to be depended upon, as it has, 

 of course, a tendency to shriidv the tissues. 



Of staining reagents, Guenaciieh's alcohoHc sohition of Horax- 

 Carniine was found to give the best results, especially after picro- 

 sulphuric acid : the Majjles solution was also useful. Various other 

 stains were employed, but were less satisfactory. 



'J'he objects, after dehydration, were treated with oil of berganiot 

 before turpentine, and were imbedded in hard i)araftin. The sections 

 were cut with a Cambridge Seien titic Instrument Conii)any's rocking 

 microtome. 



My observations, although made chiefly upon the Herring, extend 

 also to the brains of the Sprat, and Viviparous lîlenny, whilst 1 have 

 enriched my paper by fretiuent references to Mc Intosh aud Prince's 

 work upon the Wolf-iish and other forms. With reference to one 

 point, viz. the homology of the lamina terminalis, I iuive also made 

 and examined sections of larval and adult amphibians {liana, Bufo 

 aud Lissotriton). 



I. Newly-hatclie«i or early larval stage. 



Plate XXIX, figures 1—7. Woodcut-figs. 1 and 2. 



At this stage, owing to the general conformation of the head, 

 a strong flexure is observable in the brain; it affects the fore-brain, 

 and the front part of the mid-brain. Its extent may be judged from 

 the fact that in a series of transverse sections of a larva one day 

 old, the first part of the brain to appear in section is the pineal 

 body (fig. 1 pn.), whilst a little farther back (fig. 2), the cerebrum {ce.), 

 thalamencephalon {t.o.), 3"' ventricle {v.^i.), and mid-brain (»w. 6.), appear 

 in a single section. 



The disposition of the brain at this stage is as follows. I'he 

 short cerebral lobes project downwards and forwards, and above their 

 posterior ends are seen the tips of the optic thalami, the space be- 

 tween these being overhung by the pineal body. ']'he anterior part 

 of the mid-brain is also somewhat bent downwards. 



The third ventricle (fig. 2 v. 3.) is very large, extending forwards 

 between the cerebral lobes (ce.) and outwards between these structures 

 and the optic thalami {to.) so as to separate them laterally except 

 for a narrow cellular margin. It also extends ventrally into a fold 

 of the floor of the forebrain just in front of the optic connnissure, 

 A recess of the third ventricle (tigs. 3 and 4 r. v. 3.) is thus formed 



32* 



