446 L. S. STONE 



a broad contact with the distal end of the visceral sensory portion 

 of VII extending dorsoventrally in the cleft. Many mitotic 

 figures may be found at or near the point of contact, indicating 

 that many placodal cells are still steadily being split off to form 

 the ganglion. 



The lateral-line primordium in the lower portion of the hyo- 

 mandibular cleft has increased in depth and at the same time has 

 slightly lengthened. Its upper extremity lies along the posterior 

 border of the anlage of the balancer (fig. 7). 



The epibranchial placode of IX lies in the same position and 

 still has a narrow contact with the placodal cells of the visceral 

 sensory ganglion of IX. Over the first and second branchial clefts 

 the epibranchial placodes of X, now continuous as a single elon- 

 gated placode, are contributing large numbers of cells splitting off 

 en masse to the visceral sensory ganglion of X lying ventrally to 

 the vagus lateral-line ganglion (fig. 31). 



Along the posterior border of the ear and slightly above the 

 epibranchial placode of IX appears another rounded placode, 

 which is the primordium of the anterior portion of the occipital 

 group of lateral-line sense organs. It is in close contact with the 

 IX lateral-line ganglion (fig. 31). Posterior to this and above 

 the first branchial cleft is another rounded placode, which is the 

 primordium of the posterior portion of the occipital group of 

 lateral-line sense organs. 



In the dorsal portion of the intersegmental ridge of the first 

 and second somites is a rounded placode (fig. 7) connected by 

 placodal cells from its anteroventral margin to the lateral-line 

 ganglion of X, indicated by dotted line. This is the primordium 

 of the dorsal body line of lateral-line sense organs. On a level 

 with its ventral border an elongated club-shaped placode ex- 

 tends from the anterior border of the second somite to near the 

 posterior border of the third somite. This is the primordium of 

 the midbody line of sense organs and is connected bj'- a small 

 strand of cells at its anterior border to the posterior border of the 

 lateral-line ganglion of X. Just below the anterior extremity 

 of the primordium of the midbody line is a small rounded placode 

 lying close to the posterior extremity of the lateral-line ganglion 



