-49- 



Flg. 6 1. section through the opening of one of the 

 cell-groups, highly marnlfied, to show details in structure. 

 (Ivlag, 925 diain. ) 



Fip;, 7, FeLi j.-^-s^r-rr^. Larva of a stage betv/een those 

 represented in ^igs. 5 and 6« About 2 1/2 cm. in length. 



Fig. 8a. Transverse section through the pharynx and 

 anterior end of the thyroid in Ambly stoma, showing the latter 

 as a deep, ciliated groove in the floor of the former, (Mag. 

 240 diam. ) 



Fig. 8 b. Transverse section posterior to Fig. 8a , 

 showing the thyroid as an enclosed tube, lined with cilia, 

 (Mag. 240 diam, ) 



Fig. 9 a . Transverse section through the ventral half 

 of the head of an adult brook lamprey, to shov;- the position 

 and relative size of the paired salivary or basilar gland, 

 (llag, about 17 diam.) 



Fig. 9b, Transverse section through one side of the 

 salivary or basilar gland and its duct, just anterior to the 

 opening of the latter into the former, (Mag, 50 diam,) 



Fi^, 10 a. Transverse section through the ventral 

 half of an adult brock lamprey, cutting through the fourth gill 

 sacs, to shov^ the position and relative size of the thyroid gland, 

 (Mag, 30 diam,) 



Fig, 10 b _ . Transverse section through the thyroid 

 at about the plane of the section represented in Fig. 10 a, 

 (Mag. 430 diam, ) 



