488 



ERNEST W. L. HOLT, 



noticed very shortly above, has undergone considerable increase since 

 the last stage: instead of terminating in the dorsal region a little 

 behind the optic lobes (cf. fig. 10 cb.) it is elongated, and much thicker 

 in the posterior region, which is bent at an obtuse angle to the anterior 

 part (see woodcut-fig. 3). The posterior extremity is bent upwards 

 somewhat sharply, and passes into the thin roof of the fourth ven- 

 tricle {t.v.4.) which is thrown into folds by the backward extension 

 of the cerebellum. The vesicular matter of the latter is divided into 



t.c. t.l.o. v.o. a.f. 



t.v.i. 



f.g. aq. 



Fig. 3. Vertical longitudinal section of cerebellum of ^ inch herring. Z. D, Oc. 2 

 cam. lue. a.f. fibrous area of cerebellum, aq. aqueduct of Sylvids, c.aq. commissure 

 of ditto, f. g. valvula, t. c. roof of optic ventricle, 1. 1, o. tectum lobi optici, t. v. 4. roof 

 of 4*'» ventricle, v. o. optic ventricle, v. 4. 4tli ventricle. 



a thin dorsal and a thicker ventral stratum by the intervention of 

 a considerable fibrous area (a.f.). 



In the anterior half of the structure a fibrous band (c. aq.), as 

 in AnarrMchas (cf. 6, p. 915) crosses over the aqueduct of Sylvius {aq.) 

 to the lateral regions of the cerebral mass. It is immediately succeeded 

 by a smaller band, where lateral extremities are fused with those of 

 the first named. 



IV. I inch stage. 



Plate XXX, figs. 12, 13, 14, 15, 16 and 16 a. Woodcut-fig. 4. 



The olfactory lobes (fig. 15 I. ol.) are more elongated than in the 

 last stage, and the constriction at their point of origin is better marked 



