300 SCOTT. " [Vol. I. 



the mid-brain in late embryos ; the trigeminal has two ganglia 

 formed from the skin ; the facial has a ganglion formed in the 

 same way. This nerve supplies the first temporary gill-cleft ; the 

 auditory is in part derived from the facial; the ninth and tenth 

 nerves arise at first from several separate roots each provided 

 with a ganglion and connected with each other and with the 

 dorsal spinal nerves by means of a longitudinal commissure. 

 The ninth and tenth nerves early concentrate into a complex 

 mass. The lateral nerve is formed early, and apparently from 

 the epiblast of the skin. 



(13.) My observations on the development of the spinal nerves 

 agree entirely with the accounts of Sagemehl and Shipley. 



(14.) The epidermal sense-organs of the head and lateral line 

 are not developed in connection with the ganglia of the cerebral 

 nerves or with the lateral nerve, but at a later stage. This sepa- 

 ration is regarded as a secondary process. 



(15.) The olfactory organ is at first ventral in position, and is 

 always single and median. The rotation of the upper lip brings 

 the opening to the dorsal side of the head, and this is probably 

 the condition which produced the coalescence of the primitively 

 paired nasal pits. A glandular organ, resembling that of Jacob- 

 son, but having no communication with the mouth, is formed 

 from the postero-inferior portion of the nasal involution. 



(16.) The eye is formed as in other vertebrates, but is remark- 

 able for the very small part of the primary optic vesicles which 

 gives rise to the retina. During larval life the eye remains in 

 an undeveloped state, the retinal elements appearing only just 

 before metamorphosis. The lens-capsule is probably of meso- 

 blastic origin. No cornea is present in the larva. 



(17.) The early stages of the auditory organ do not differ in 

 any essential respect from those of the higher vertebrates ; the 

 young larva first exhibits the divergences. There is no trace of 

 the horizontal semicircular canal; the vestibule is divided imper- 

 fectly into chambers, and a median appendix is formed. The 

 recessus labyrinthi persist throughout larval life, and probably in 

 the adult. The cristae acusticae are marked in the young larva 

 by patches of epithelium bearing stiff auditory hairs. The ear 

 is relatively better developed in the larva than either of the 

 other higher organs of sense, and does not undergo such marked 

 changes at metamorphosis. 



