123 
When it is remembered that only one other ordinal type of existing 
fishes (the Dipnoan) has been discovered during the present cen- 
tury, the importance of the new group may be realized. 
2. On the Segmental Sense organs of the lateral line, and on the Mor- 
phology of the Vertebrate Auditory organ. 
By John Beard, Zool. Station, Naples. 
i eingeg. 22. Dec. 1883. 
The mode of development of the lateral nerve in fishes is still a 
disputed question. Since the commencement of my researches two 
papers have appeared in both of which the question is dealt with. 
But my own results differ very much from those obtained by Van 
Wijhe and Hoffmann — a difference not to be accounted for by 
difference of material, forHoffmann has worked upon the same genus. 
In a subsequent section of this paper I shall have occasion to draw 
certain conclusions from the researches of Van Wijhe and others on 
the cranial nerves, but on the one point of the mode of growth of the 
lateral nerve I differ very much from him. My researches lead me to 
accept the conclusion of Balfour that the lateral nerve arises just as 
all the other nerves do, and not as a splitting off of a portion of the 
epiblast. 
In the Embryo of Salmo fario , the first appearance of the lateral 
line consists in the splitting off of certain of the cells of the inner epi- 
blastic layer. This separation takes place at the level of the notochord. 
It commences in the region of the neck just behind the ear capsule 
| and opposite the hyoid arch. At its point of origin it is broad, and is 
at first short, but soon grows back longitudinally along the whole length 
of the body. This cord of cells gives origin to the sense organs of the 
lateral line. 
When the cord is completely established along the whole body it 
presents the following characters. In the region of the neck it is broad, 
thinning out a little further back about opposite the hinder end of the 
anterior fin. In each segment of the body from this point backwards 
it presents a thickening, the cord between these consecutive thicken- 
ings being thin and composed of one layer of cells. The thickenings 
in the body are much smaller in breadth and extent than the anterior 
thickening in the region of the neck. 
À transverse section in the region of one of these thickenings 
shows a somewhat oval plate of two layers of large oval cells. In the 
intermediate region the rod in section consists of only one narrow layer 
of cells. In the subsequent growth of the embryo the intermediate 
