THE CARPS 39 



The serial section Plate 5, Fig. i, shows the vagal lobes, which 

 are very small compared with the vagals of the roach, as figured in 

 Plate 4, Fig. i. The fii'st lobe to produce a definite prominence 

 dorsally in Engraulcypris is the Vtli or somatic- sensory lobe, and on 

 either side this lobe hides the vagal as seen in Plate 5, Fig. ii. The 

 vagals are here club-shaped in section, with the rounded dorsal 

 portions tending to meet in the middle Une. In Plate 5, Fig. iii, 

 the junction is complete., and the fifth lobe have also approached 

 the middle line. The presence of a small facial lobe is now recognised 

 by descending fibres passing from the central lobe, formed posteriorly 

 by the united vagals, but now formed by the medium fusion of two 

 very small facial lobes. Descending fibres passing laterally down- 

 wards and out"s\"ards into the great longitudinal secondary gustatory 

 tracts, an important bundle very obvious in the cjrprinoicl medulla. 



This identification of the facial lobes is confirmed if the section 

 shown in Plate 5, Figs, v and vi are examined. In Fig. v, the Vllth or 

 facial nerve is seen cut in section, and in Fig. vi the same nerve is seen 

 cut horizontally as it passes in its usual course from the periphery 

 to the margin of the ventricle. To enable the reader to follow the 

 differences in the medullae of the roach and the plankton-feeding 

 type as illustrated by EngrauHcypris we will summarise the matter. 



In the roach the naked eye examination shows two lateral pro- 

 minences posteriorly the vagal lobes, and these embrace anteriorly 

 a small facial lobe. The sections confirm this picture ; in Engrauli- 

 cj^pris neither vagal nor facial lobes are seen superficially and can 

 only be recognised microscopically. 



We now come to that part of the brain wliich hes between the 

 medulla and the optic lobes and consists of the cerebellum and its 

 lateral supports connecting it with the medulla, which give rise to 

 the prominences known as the acoustic tubercles or the acoustico- 

 lateralis areas. These can be seen on either side of the base of the 

 cerebellum in Plates 4 and 5, Fig. vi. The acoustic tubercles 

 receive afferent fibres from the eighth nerve or auditory and from 

 the laterahs nerve which is the nerve of the organs of the lateral 

 Une of which we shall speak later. The function of the cerebellum 

 and acoustic tubercles has been the subject of a great deal of 

 theoretical speculation, but the former is usually held to be associated 

 with the perception of position in space, as recorded by the semi- 

 circular canals of the internal ear. The cerebellum may be simply 

 a globular protuberance or may be tongue-shaped, but it always has 

 a characteristic internal structure ; it has a core which consists of 

 darkly staining cells, called the stratum granulosum, which is 

 surrounded by a marginal layer of pecuhar cells, which lie in an 



