356 DEEP SEA FISHES. 



which lack the extraordinary filamentary productions and on which the Lat- 

 eral System is evidently of much greater functional importance and develop- 

 ment. This will be made evident beyond the need of further remark by 

 contrasting Plates F and LXXV. of Dicrolene, and fig. 1 of Plate K, 

 and Plate LV. of Bathypterois, with Plate XXXIV. and fig. 1 of Plate 

 LXXXI. of Lamprogrammus, Plates XXXV. and LXXIX. of Eretmichthys, 

 and Plate LXXVII. of Bassozetus. Another instance that may be noted is 

 that of Leucicorns, Plates XXXVIII. and LXXIY. fig. 1, a fish without fila- 

 mentary organs, and with few prominently developed sensory papillae, and 

 one on which the eyes, probably functional early in life, are liable to deteri- 

 oration in older individuals ; on this fish the organs of the Lateral System 

 attain a maximum size and a paramount differentiation. 



There appears to be no connection between one disk and another, pos- 

 sibly it is invisible, on many species but on the more differentiated a very 

 evident thread-like connection exists, Plate XLI. figs, l"* and 2"^ and on some 

 of them the more common nerve-like thread is accompanied in its course by 

 a considerable number of minute nerves. Plates XXXVIII. fig. 7, and 

 XXXIX. fig. 2. Plates XXXIV. figs. 4 and 5 and XLI. figs. P and 2" repre- 

 sent the more common appearance of the disks on forms in which the devel- 

 opment has not been carried to such an extraordinary degree. A transitory 

 connection between the disks in certain embryos is mentioned by AUis. 



The main nerve to each disk extends to the back, that is to the inner 

 side of the central body and there sends out a number of small branches, 

 varying for different disks, individuals and species; these branches distribute 

 themselves irregularly through the rounded or oblong centrum, and from it 

 into ths lateral portions of the fusiform mass upon which it is situated. An 

 approximate idea of the manner of the distribution within the fusiform 

 transverse body and the included centrum may be gained from fig. 4 on 

 Plate XXXV. In this case, Eretmichthys, the number of nervules leaving 

 the centrum is comparatively small ; it represents an intermediate between 

 those cases in which none are to be observed and those like figure 7, of 

 Plate XXXVIII., in which there are many. From the anterior and the pos- 

 terior edges of the fusiform mass, in some species at least, the nervules pass 

 into other masses, one mass at each side of the fusiform. The latter give 

 to the disk in its entirety a longitudinally oblong shape, Plate XXXVIII. 

 figs. 7 and 3, and Plate XXXIX. fig. 2. Whatever they may have been 

 in life these jiortions of the oigan are more opaque and whitish than the 



