ORIGIN OF THE LATERAL LINE PRIMORDIA 



583 



THE 10-MM. EMBRYO 



Before taking up the problem of the origin of the lateral lines 

 it seems advisable to give a brief description of some advanced 

 stage of the lateral lines. For this we have chosen the 10-mm. 

 embryo which is the same as that plotted by Landacre ('12). 

 Plate 1 of his paper should be consulted for a general description 

 of the nerves and ganglia of a 10-mm. embryo. The three sen- 

 sory lines of the head are present at this st^ge (fig. 6 of the present 

 paper) . The supra-orbital line extends from a point about mid- 

 way between the optic vesicle and the auditory vesicle cephalad 

 and dorsad in a gentle curve until it ends in the region imme- 

 diately dorsal to the anterior end of the optic vesicle. The cells 



TABLE 1 



Showing age, length, increment in age and length of embryos of Lepidosteus 



