254 HENRY C. TRACY 



Fig. 15 Microscopic section of the head of Stolephorus, 28 mm. in length. 

 The section is sagittal and is taken about one-third the distance between the 

 median plane and the lateral side of the head. The otic capsule is still cartilag- 

 inous, though membrane bone formation has begun on the surface. There is 

 only one membranous vesicle (MV) at this stage. The canal (CSD) for the pre- 

 coelomic diverticulum passes through the cartilage of the otic capsule. The 

 diverticulum itself is cut obliquely (PSB) just before its entrance to the mem- 

 branous vesicle. The vesicle occupies a space excavated from the cartilage of 

 the otic capsule; beginning of bone formation in the connective tissue around 

 the vesicle has taken place. 



Fig. 16 Dissection of the occipital region of the skull to show the position 

 of the supracerebral perilabyrinthine band. Pomolobus pseudoharengus. 



