EMBItYOLOGY OF THE SEA BASS. 
249 
gradual obliteration by the elongation of the connecting strand. Fig. 121 shows 
the character of the strand commonly met with, in which the cells have no especial 
arrangement. The connecting strand continues to elongate, because of the backward 
growth of the posterior imrtiou of the original anlage, until it becomes excessively 
thin and finally disappears. At the time of hatching I am unable to find any trace 
of it. However, my inability to trace the origin of nerves in the Bass shows that the 
apparent disappearance of the strand is not a conclusive argument against the sup- 
position (Beard, 6 ) that it may persist as a fine nerve thread. 
The posterior of the two parts into which the first constriction separates the orig- 
inal anlage is, as I have said, the larger of the two. In transverse section it presents 
about the same appearance as the anterior organ in Fig. 113, PI. ci. Its cavity is, 
however, a much elongated one (Fig. 150, right side). This portion of the primitive 
sac sutlers a constriction which begins before the first connecting strand has disap- 
l)eared (Fig. 150, left side). Of the two parts into which it is separated the anterior 
{1. 1. 0 ^, Fig. 150, left) becomes the second lateral line organ. The condition of this 
organ at the time of constriction is fairly represented by Fig. 120, PL cii. Its cavity 
subsequently disappears, and at the time of hatching it is a histologically differen- 
tiated organ {1. 1. oL, Fig. 126, PI. cii), lying just in front of the anus. 
The posterior pait of the original anlage, which the secoud constriction pinches 
oft' (Fig. 150, left), presents at first about the same appearance iu section as the organ 
shown in Fig. 120, PI. oil. It lies in front of the anus. At the time of hatching, 
some 10 hours after the constriction begins, this portion of the lateral line anlage 
forms a rod of cells lying behind the anus, on which sometimes one, sometimes two, 
sense organs are found in process of forming. The rod lies like the sense organs in 
front of it, along the middle line of the lateral surface, and I could not distinguish it 
in surface preparations. The series of sections, 12G‘-12G‘'", PL cm, however, satis- 
factorily elucidates its nature. Each section represents the lateral line region of the 
opposite sides. Glancing through the series it will be seen that the rods do not lie 
exactly opposite each other, and that moreover on one side two sense organs are indi- 
cated, on the other but one. The section 12G* is the most anterior of the series and 
shows that on the left side the rod does not extend so far iu front, while on the right 
there is a sense cord (s. c.) which, however, extends but a short distance in front of 
the sense organ (L 1. O 3 , 126“) and must be regarded as the anterior end of that organ. 
Fig. 126“ lies four sections farther back. On the left there is no sense cord ; on the 
right there is a sense organ {1. 1. O3.) in process of forming. It is in about the same 
stage as that of Fig. 120. Going backwards from Fig. 126“ to 126“‘ the sense organ on 
the right gradually passes into the connecting strand {go 7 i. st.) ; on the left a shoit rod 
of cells is first met with which proves to be the anterior end of the sense organ, 1. 1. 03 L 
Continuing back from 126“^ to 126*'" on the right, the connecting strand passes into 
another incipient sense organ, 1. 1. 04 ., but on the left there is behind the organ, 1. 1. 03 L, 
nothing but a simple cord of cells, which comes to an end not far behind 126*L The 
organ L 1. 04 . is likewise prolonged backwards as a short cord of cells. In no part of 
the postanal sense tract on either side has histological modification set in. 
From the series of sections it is plain that the cord of cells on the right is suffer- 
ing constriction and is thus giving rise to two organs, 1. 1. O 3 . and 1. 1. O 4 . On the left 
there is no constriction and but one organ is forming. The cavity in each of these 
