No. 3.] LATERAL LINE OF AMIA. STI 
ening, a part of it, however, passing on as the future postbran- 
chial nerve to the lateral muscle-plate of the segment. At the 
point of fusion, cells are rapidly proliferated. The deeper part 
of the mass which thus arises is the rudiment of the ganglion 
of the dorsal root, and the superficial portion, the rudiment of a 
branchial sense-organ. The deeper portion soon separates from 
the rest of the mass, leaving a nerve strand connecting it with 
sensory portion, and, lying deeper in the mesoblast on the root 
of the nerve, apparently at first distal to the point of separation 
of the post-branchial branch, becomes the ganglion of the nerve. 
The superficial sensory part of the thickening may remain 
very small, or it may increase to a very considerable length, 
pushing its way either backward or forward, as the case may 
be, between the general epiblast cells, and connected in every 
case with the ganglion of the segment by the supra-branchial 
nerve, which is split off from under side of the thickening 
simultaneously with its growth. Along this thickening, con- 
comitantly with the splitting off of the nerve, different organs 
arise, according to Beard, by the simple and repeated division 
of the single organ formed over the cleft, each organ so formed 
being connected by a separate branch with the main supra- 
branchial nerve. 
This method of origin differs somewhat from that of the 
lateral line of Salmo, where, according to Hoffman (No. 8, p. 
88), the different sense-organs arise independently after the 
lateral nerve has been split off from the under part of the 
epiblastic thickening which represents the line. As the nerve 
separates, a strand is left at each intermuscular septum con- 
necting the nerve with the cells of the deeper part of the epi- 
dermis where later the organ will arise. 
Beard’s work was mainly confined to Torpedo ocellata, but he 
confirmed the results obtained in this form by comparison with 
the embryos of Mustelus and Pristiurus, and of certain Teleostei 
and Amphibia. In all these forms he finds seven supra-bran- 
chial nerves and seven corresponding lines of branchial sense- 
organs ; but the position of these organs in the embryos is not 
fully detailed, and the adult conditions are not noticed at all, so 
that it is impossible to tell what becomes of the seven thicken- 
ings, and where, in the adult, the organs developed from each 
are to be found. 
