GANOIDEI. 



117 



The first of Agassiz' embryos was hatched about ten days 

 after impregnation. The young fish on hatching immediately 

 used its suctorial disc to attach itself to the sides of the vessel in 

 which it was placed. 



The general form of 

 Lepidosteus shortly after 

 hatching is shewn in fig. 

 67. On the ventral part 

 of the front of the head 

 is placed the large sucto- 

 rial disc. At the side of 

 the head are seen the 

 olfactory pit, the eye and 

 the auditory vesicle; while 

 the projecting vesicle of 



the mid-brain is very pro- 



FIG. 66. VENTRAL VIEW OF THE HEAD OF 

 A LEPIDOSTEUS EMBRYO SHORTLY BEFORE 

 HATCHING, TO SHEW THE LARGE SUCTORIAL 



DISC. 



HI. mouth; op. eye; s.d. suctorial disc. 



sd 



op 



minent above. Behind 

 the mouth follow the vis- 

 ceral arches. The man- 



dibular arch (aid] is 

 placed on the hinder border of the mouth, and is separated by a 

 deep groove from the hyoid arch (?iy). This groove is connected 

 with the hyomandibular cleft, but I have not determined whether 



sd 



by 



FIG. 67. LARVA OF LEPIDOSTEUS SHORTLY AFTER HATCHING. (After Parker.) 

 ol. olfactory pit ; op. optic vesicle ; au.v. auditory vesicle ; mb. mid-brain ; 

 sd. suctorial disc; md. mandibular arch ; hy. hyoid arch with operculum ; br. branchial 

 arches; an. anus. 



it is now perforated. The posterior border of the hyoid arch is 

 prolonged into an opercular fold. Behind the hyoid arch are 

 seen the true branchial arches. 



