358 DEEP SEA FISHES. 



branches unite on the occii^ut, and the majority of the other types figured 

 below wliich possess disunited auruls and a frontal cranial branch that tends 

 toward the formation of a loop, as on Laniprogranimus, Plate XXXIV. fig. 3, 

 and Plate LXXXI. fig. 1. Aniia has the occipital commissure of the aural 

 branches ; it also possesses the frontal branch backward from the cranial 

 toward the aural. For the arrangement and innervation of the system on 

 Amia see the work of Allis, 1889, fig. 49. On the body of the teleostean 

 the sj'stera varies from the complete, extending along the body from head 

 to tail, to partial or entire absence, to interrupted series, or to several 

 duplicate rows, and from lines of simple nerve papillae to those of exces- 

 sively modified disks, and the drafts upon the vagus vary accordingly. 



Turning attention especially to the cephalic organs a large amount of 

 variation in the numbers of disks will be at once apparent; on the species 

 sketched the range is from fifty disks up to ninety. Further than this, 

 many species have disks of different sizes or of different degrees of develop- 

 ment on different parts of the head. This diversity is a consequent of par- 

 ticular habits ; species on which the function of the disks is equally important 

 in all directions have the organs about equally developed on the top of the 

 head on the sides and beneath, as Mixonus, Porogadus, Bassogigas, and 

 Catajtyx of Plates LXXIV., LXXVI., and LXXX. ; but others on which the 

 function upward accords better with the habits have large disks on the upper 

 parts of the head and small ones on the lower, as Bassosdus nasus, Plate 

 LXXVII. and species of Eretmichthys, Plate LXXIX. ; and still others as 

 the Halosauroids, Plate LXXXIV. fig. 1, find a function downward more sat- 

 isfying to their necessities and possess disks of extraordinary development 

 on the lower portions of the head and the body while those of the upper 

 parts have suffered from neglect. Some of the species have the disks hid- 

 den by darkly pigmented mantles from all directions except below ; this is 

 particularly the case on species of the subgenus Halosaiu'opsis. A wide 

 range of perfection in the system is to be seen on the species of Halosaurus : 

 on forms like 77. attenuahis, Plate LX. fig. 1, the disks and their envelopes 

 are so thin as to be almost invisible and so delicately attached to the sur- 

 faces of the scales as to be carried away by a very slight rub ; on U. radia- 

 ius Plate LX. fig. 2, a much greater degree of advancement obtains ; and on 

 11. macrochir and H. rostratus the mechanism appears to have reached the 

 extreme of differentiation. On these last the disks and the particular scale 

 on which each is seated are much enlarged and the dark mantle by which 



