258 G. E. COGHILL 



A. THE NON-MOTILE STAGE 



1. The lateral line component. The position and extent of 

 development of the primordia of the various lateral lines of the 

 head are shown in Paper I, figure 56 (Pr.LL.). The primordium 

 of the preauditory lines consists of a single boot-shaped patch 

 of thickened epithelium: the toe of the 'boot' extending forward 

 and a little dorsad as the beginning of the supraorbital line 

 and the heel projecting ventrad as the beginning of the infra- 

 orbital line. From the caudal end of this structure a narrow 

 strip of thickened epithelium connects it with the auditory 

 vesicle, which still has a broad attachment with the skin (fig. 

 73, Ad.,Aud.V). This slender connective between the auditory 

 vesicle and the lateral line primordium has the structure of the 

 thickening of ectoderm which persists for a time after the ophth- 

 almic ganglion detaches itself from the skin. It may represent 

 the area of origin of a dorso-lateral placode, although I have no 

 conclusive evidence of this. 



The facial lateral line ganglia of this stage are rather loose 

 masses of cells to which only indefinite borders can be estab- 

 lished (fig. 1). The mass of cells which represents the hyo- 

 mandibular division of the nerve extends a considerable distance 

 caudad under the auditory vesicle, with which it seems to be 

 fused in a small area near the auditory ganglion. From this 

 region it projects laterad and rostrad as a loose collection of cells 

 which has a very indefinite relation to the skin. The other 

 lateral line facial ganglion, which later gives rise to the r. ophthal- 

 micus superficialis VII and r. buccalis VII has a more definite 

 outhne and is somewhat more highly differentiated. It holds a 

 more dorsal position and extends rostrad to the lateral line pri- 

 mordium, with which it is in direct contact. A considerable 

 number of fibers from the ganglion attach themselves to the pri- 

 mordium, upon which they can be traced for only a very short 

 distance. 



The lateral line ganglia have root fibers which reach to the 

 surface of the brain at about the level of the rostral border of the 



